diff --git a/BUILD b/BUILD
index f62f70651b1..dca5c8cdee0 100644
--- a/BUILD
+++ b/BUILD
@@ -878,6 +878,15 @@ grpc_cc_library(
     deps = ["gpr_platform"],
 )
 
+grpc_cc_library(
+    name = "switch",
+    language = "c++",
+    public_hdrs = [
+        "src/core/lib/promise/detail/switch.h",
+    ],
+    deps = ["gpr_platform"],
+)
+
 grpc_cc_library(
     name = "ref_counted",
     language = "c++",
diff --git a/src/core/lib/promise/detail/switch.h b/src/core/lib/promise/detail/switch.h
new file mode 100644
index 00000000000..f164e23c4da
--- /dev/null
+++ b/src/core/lib/promise/detail/switch.h
@@ -0,0 +1,1455 @@
+/*
+ * Copyright 2021 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * Automatically generated by tools/codegen/core/gen_switch.py
+ */
+
+#ifndef GRPC_CORE_LIB_PROMISE_DETAIL_SWITCH_H
+#define GRPC_CORE_LIB_PROMISE_DETAIL_SWITCH_H
+
+#include <grpc/impl/codegen/port_platform.h>
+
+#include <stdlib.h>
+
+namespace grpc_core {
+
+template <typename R, typename F0>
+R Switch(char idx, F0 f0) {
+  switch (idx) {
+    case 0:
+      return f0();
+  }
+  abort();
+}
+
+template <typename R, typename F0, typename F1>
+R Switch(char idx, F0 f0, F1 f1) {
+  switch (idx) {
+    case 0:
+      return f0();
+    case 1:
+      return f1();
+  }
+  abort();
+}
+
+template <typename R, typename F0, typename F1, typename F2>
+R Switch(char idx, F0 f0, F1 f1, F2 f2) {
+  switch (idx) {
+    case 0:
+      return f0();
+    case 1:
+      return f1();
+    case 2:
+      return f2();
+  }
+  abort();
+}
+
+template <typename R, typename F0, typename F1, typename F2, typename F3>
+R Switch(char idx, F0 f0, F1 f1, F2 f2, F3 f3) {
+  switch (idx) {
+    case 0:
+      return f0();
+    case 1:
+      return f1();
+    case 2:
+      return f2();
+    case 3:
+      return f3();
+  }
+  abort();
+}
+
+template <typename R, typename F0, typename F1, typename F2, typename F3,
+          typename F4>
+R Switch(char idx, F0 f0, F1 f1, F2 f2, F3 f3, F4 f4) {
+  switch (idx) {
+    case 0:
+      return f0();
+    case 1:
+      return f1();
+    case 2:
+      return f2();
+    case 3:
+      return f3();
+    case 4:
+      return f4();
+  }
+  abort();
+}
+
+template <typename R, typename F0, typename F1, typename F2, typename F3,
+          typename F4, typename F5>
+R Switch(char idx, F0 f0, F1 f1, F2 f2, F3 f3, F4 f4, F5 f5) {
+  switch (idx) {
+    case 0:
+      return f0();
+    case 1:
+      return f1();
+    case 2:
+      return f2();
+    case 3:
+      return f3();
+    case 4:
+      return f4();
+    case 5:
+      return f5();
+  }
+  abort();
+}
+
+template <typename R, typename F0, typename F1, typename F2, typename F3,
+          typename F4, typename F5, typename F6>
+R Switch(char idx, F0 f0, F1 f1, F2 f2, F3 f3, F4 f4, F5 f5, F6 f6) {
+  switch (idx) {
+    case 0:
+      return f0();
+    case 1:
+      return f1();
+    case 2:
+      return f2();
+    case 3:
+      return f3();
+    case 4:
+      return f4();
+    case 5:
+      return f5();
+    case 6:
+      return f6();
+  }
+  abort();
+}
+
+template <typename R, typename F0, typename F1, typename F2, typename F3,
+          typename F4, typename F5, typename F6, typename F7>
+R Switch(char idx, F0 f0, F1 f1, F2 f2, F3 f3, F4 f4, F5 f5, F6 f6, F7 f7) {
+  switch (idx) {
+    case 0:
+      return f0();
+    case 1:
+      return f1();
+    case 2:
+      return f2();
+    case 3:
+      return f3();
+    case 4:
+      return f4();
+    case 5:
+      return f5();
+    case 6:
+      return f6();
+    case 7:
+      return f7();
+  }
+  abort();
+}
+
+template <typename R, typename F0, typename F1, typename F2, typename F3,
+          typename F4, typename F5, typename F6, typename F7, typename F8>
+R Switch(char idx, F0 f0, F1 f1, F2 f2, F3 f3, F4 f4, F5 f5, F6 f6, F7 f7,
+         F8 f8) {
+  switch (idx) {
+    case 0:
+      return f0();
+    case 1:
+      return f1();
+    case 2:
+      return f2();
+    case 3:
+      return f3();
+    case 4:
+      return f4();
+    case 5:
+      return f5();
+    case 6:
+      return f6();
+    case 7:
+      return f7();
+    case 8:
+      return f8();
+  }
+  abort();
+}
+
+template <typename R, typename F0, typename F1, typename F2, typename F3,
+          typename F4, typename F5, typename F6, typename F7, typename F8,
+          typename F9>
+R Switch(char idx, F0 f0, F1 f1, F2 f2, F3 f3, F4 f4, F5 f5, F6 f6, F7 f7,
+         F8 f8, F9 f9) {
+  switch (idx) {
+    case 0:
+      return f0();
+    case 1:
+      return f1();
+    case 2:
+      return f2();
+    case 3:
+      return f3();
+    case 4:
+      return f4();
+    case 5:
+      return f5();
+    case 6:
+      return f6();
+    case 7:
+      return f7();
+    case 8:
+      return f8();
+    case 9:
+      return f9();
+  }
+  abort();
+}
+
+template <typename R, typename F0, typename F1, typename F2, typename F3,
+          typename F4, typename F5, typename F6, typename F7, typename F8,
+          typename F9, typename F10>
+R Switch(char idx, F0 f0, F1 f1, F2 f2, F3 f3, F4 f4, F5 f5, F6 f6, F7 f7,
+         F8 f8, F9 f9, F10 f10) {
+  switch (idx) {
+    case 0:
+      return f0();
+    case 1:
+      return f1();
+    case 2:
+      return f2();
+    case 3:
+      return f3();
+    case 4:
+      return f4();
+    case 5:
+      return f5();
+    case 6:
+      return f6();
+    case 7:
+      return f7();
+    case 8:
+      return f8();
+    case 9:
+      return f9();
+    case 10:
+      return f10();
+  }
+  abort();
+}
+
+template <typename R, typename F0, typename F1, typename F2, typename F3,
+          typename F4, typename F5, typename F6, typename F7, typename F8,
+          typename F9, typename F10, typename F11>
+R Switch(char idx, F0 f0, F1 f1, F2 f2, F3 f3, F4 f4, F5 f5, F6 f6, F7 f7,
+         F8 f8, F9 f9, F10 f10, F11 f11) {
+  switch (idx) {
+    case 0:
+      return f0();
+    case 1:
+      return f1();
+    case 2:
+      return f2();
+    case 3:
+      return f3();
+    case 4:
+      return f4();
+    case 5:
+      return f5();
+    case 6:
+      return f6();
+    case 7:
+      return f7();
+    case 8:
+      return f8();
+    case 9:
+      return f9();
+    case 10:
+      return f10();
+    case 11:
+      return f11();
+  }
+  abort();
+}
+
+template <typename R, typename F0, typename F1, typename F2, typename F3,
+          typename F4, typename F5, typename F6, typename F7, typename F8,
+          typename F9, typename F10, typename F11, typename F12>
+R Switch(char idx, F0 f0, F1 f1, F2 f2, F3 f3, F4 f4, F5 f5, F6 f6, F7 f7,
+         F8 f8, F9 f9, F10 f10, F11 f11, F12 f12) {
+  switch (idx) {
+    case 0:
+      return f0();
+    case 1:
+      return f1();
+    case 2:
+      return f2();
+    case 3:
+      return f3();
+    case 4:
+      return f4();
+    case 5:
+      return f5();
+    case 6:
+      return f6();
+    case 7:
+      return f7();
+    case 8:
+      return f8();
+    case 9:
+      return f9();
+    case 10:
+      return f10();
+    case 11:
+      return f11();
+    case 12:
+      return f12();
+  }
+  abort();
+}
+
+template <typename R, typename F0, typename F1, typename F2, typename F3,
+          typename F4, typename F5, typename F6, typename F7, typename F8,
+          typename F9, typename F10, typename F11, typename F12, typename F13>
+R Switch(char idx, F0 f0, F1 f1, F2 f2, F3 f3, F4 f4, F5 f5, F6 f6, F7 f7,
+         F8 f8, F9 f9, F10 f10, F11 f11, F12 f12, F13 f13) {
+  switch (idx) {
+    case 0:
+      return f0();
+    case 1:
+      return f1();
+    case 2:
+      return f2();
+    case 3:
+      return f3();
+    case 4:
+      return f4();
+    case 5:
+      return f5();
+    case 6:
+      return f6();
+    case 7:
+      return f7();
+    case 8:
+      return f8();
+    case 9:
+      return f9();
+    case 10:
+      return f10();
+    case 11:
+      return f11();
+    case 12:
+      return f12();
+    case 13:
+      return f13();
+  }
+  abort();
+}
+
+template <typename R, typename F0, typename F1, typename F2, typename F3,
+          typename F4, typename F5, typename F6, typename F7, typename F8,
+          typename F9, typename F10, typename F11, typename F12, typename F13,
+          typename F14>
+R Switch(char idx, F0 f0, F1 f1, F2 f2, F3 f3, F4 f4, F5 f5, F6 f6, F7 f7,
+         F8 f8, F9 f9, F10 f10, F11 f11, F12 f12, F13 f13, F14 f14) {
+  switch (idx) {
+    case 0:
+      return f0();
+    case 1:
+      return f1();
+    case 2:
+      return f2();
+    case 3:
+      return f3();
+    case 4:
+      return f4();
+    case 5:
+      return f5();
+    case 6:
+      return f6();
+    case 7:
+      return f7();
+    case 8:
+      return f8();
+    case 9:
+      return f9();
+    case 10:
+      return f10();
+    case 11:
+      return f11();
+    case 12:
+      return f12();
+    case 13:
+      return f13();
+    case 14:
+      return f14();
+  }
+  abort();
+}
+
+template <typename R, typename F0, typename F1, typename F2, typename F3,
+          typename F4, typename F5, typename F6, typename F7, typename F8,
+          typename F9, typename F10, typename F11, typename F12, typename F13,
+          typename F14, typename F15>
+R Switch(char idx, F0 f0, F1 f1, F2 f2, F3 f3, F4 f4, F5 f5, F6 f6, F7 f7,
+         F8 f8, F9 f9, F10 f10, F11 f11, F12 f12, F13 f13, F14 f14, F15 f15) {
+  switch (idx) {
+    case 0:
+      return f0();
+    case 1:
+      return f1();
+    case 2:
+      return f2();
+    case 3:
+      return f3();
+    case 4:
+      return f4();
+    case 5:
+      return f5();
+    case 6:
+      return f6();
+    case 7:
+      return f7();
+    case 8:
+      return f8();
+    case 9:
+      return f9();
+    case 10:
+      return f10();
+    case 11:
+      return f11();
+    case 12:
+      return f12();
+    case 13:
+      return f13();
+    case 14:
+      return f14();
+    case 15:
+      return f15();
+  }
+  abort();
+}
+
+template <typename R, typename F0, typename F1, typename F2, typename F3,
+          typename F4, typename F5, typename F6, typename F7, typename F8,
+          typename F9, typename F10, typename F11, typename F12, typename F13,
+          typename F14, typename F15, typename F16>
+R Switch(char idx, F0 f0, F1 f1, F2 f2, F3 f3, F4 f4, F5 f5, F6 f6, F7 f7,
+         F8 f8, F9 f9, F10 f10, F11 f11, F12 f12, F13 f13, F14 f14, F15 f15,
+         F16 f16) {
+  switch (idx) {
+    case 0:
+      return f0();
+    case 1:
+      return f1();
+    case 2:
+      return f2();
+    case 3:
+      return f3();
+    case 4:
+      return f4();
+    case 5:
+      return f5();
+    case 6:
+      return f6();
+    case 7:
+      return f7();
+    case 8:
+      return f8();
+    case 9:
+      return f9();
+    case 10:
+      return f10();
+    case 11:
+      return f11();
+    case 12:
+      return f12();
+    case 13:
+      return f13();
+    case 14:
+      return f14();
+    case 15:
+      return f15();
+    case 16:
+      return f16();
+  }
+  abort();
+}
+
+template <typename R, typename F0, typename F1, typename F2, typename F3,
+          typename F4, typename F5, typename F6, typename F7, typename F8,
+          typename F9, typename F10, typename F11, typename F12, typename F13,
+          typename F14, typename F15, typename F16, typename F17>
+R Switch(char idx, F0 f0, F1 f1, F2 f2, F3 f3, F4 f4, F5 f5, F6 f6, F7 f7,
+         F8 f8, F9 f9, F10 f10, F11 f11, F12 f12, F13 f13, F14 f14, F15 f15,
+         F16 f16, F17 f17) {
+  switch (idx) {
+    case 0:
+      return f0();
+    case 1:
+      return f1();
+    case 2:
+      return f2();
+    case 3:
+      return f3();
+    case 4:
+      return f4();
+    case 5:
+      return f5();
+    case 6:
+      return f6();
+    case 7:
+      return f7();
+    case 8:
+      return f8();
+    case 9:
+      return f9();
+    case 10:
+      return f10();
+    case 11:
+      return f11();
+    case 12:
+      return f12();
+    case 13:
+      return f13();
+    case 14:
+      return f14();
+    case 15:
+      return f15();
+    case 16:
+      return f16();
+    case 17:
+      return f17();
+  }
+  abort();
+}
+
+template <typename R, typename F0, typename F1, typename F2, typename F3,
+          typename F4, typename F5, typename F6, typename F7, typename F8,
+          typename F9, typename F10, typename F11, typename F12, typename F13,
+          typename F14, typename F15, typename F16, typename F17, typename F18>
+R Switch(char idx, F0 f0, F1 f1, F2 f2, F3 f3, F4 f4, F5 f5, F6 f6, F7 f7,
+         F8 f8, F9 f9, F10 f10, F11 f11, F12 f12, F13 f13, F14 f14, F15 f15,
+         F16 f16, F17 f17, F18 f18) {
+  switch (idx) {
+    case 0:
+      return f0();
+    case 1:
+      return f1();
+    case 2:
+      return f2();
+    case 3:
+      return f3();
+    case 4:
+      return f4();
+    case 5:
+      return f5();
+    case 6:
+      return f6();
+    case 7:
+      return f7();
+    case 8:
+      return f8();
+    case 9:
+      return f9();
+    case 10:
+      return f10();
+    case 11:
+      return f11();
+    case 12:
+      return f12();
+    case 13:
+      return f13();
+    case 14:
+      return f14();
+    case 15:
+      return f15();
+    case 16:
+      return f16();
+    case 17:
+      return f17();
+    case 18:
+      return f18();
+  }
+  abort();
+}
+
+template <typename R, typename F0, typename F1, typename F2, typename F3,
+          typename F4, typename F5, typename F6, typename F7, typename F8,
+          typename F9, typename F10, typename F11, typename F12, typename F13,
+          typename F14, typename F15, typename F16, typename F17, typename F18,
+          typename F19>
+R Switch(char idx, F0 f0, F1 f1, F2 f2, F3 f3, F4 f4, F5 f5, F6 f6, F7 f7,
+         F8 f8, F9 f9, F10 f10, F11 f11, F12 f12, F13 f13, F14 f14, F15 f15,
+         F16 f16, F17 f17, F18 f18, F19 f19) {
+  switch (idx) {
+    case 0:
+      return f0();
+    case 1:
+      return f1();
+    case 2:
+      return f2();
+    case 3:
+      return f3();
+    case 4:
+      return f4();
+    case 5:
+      return f5();
+    case 6:
+      return f6();
+    case 7:
+      return f7();
+    case 8:
+      return f8();
+    case 9:
+      return f9();
+    case 10:
+      return f10();
+    case 11:
+      return f11();
+    case 12:
+      return f12();
+    case 13:
+      return f13();
+    case 14:
+      return f14();
+    case 15:
+      return f15();
+    case 16:
+      return f16();
+    case 17:
+      return f17();
+    case 18:
+      return f18();
+    case 19:
+      return f19();
+  }
+  abort();
+}
+
+template <typename R, typename F0, typename F1, typename F2, typename F3,
+          typename F4, typename F5, typename F6, typename F7, typename F8,
+          typename F9, typename F10, typename F11, typename F12, typename F13,
+          typename F14, typename F15, typename F16, typename F17, typename F18,
+          typename F19, typename F20>
+R Switch(char idx, F0 f0, F1 f1, F2 f2, F3 f3, F4 f4, F5 f5, F6 f6, F7 f7,
+         F8 f8, F9 f9, F10 f10, F11 f11, F12 f12, F13 f13, F14 f14, F15 f15,
+         F16 f16, F17 f17, F18 f18, F19 f19, F20 f20) {
+  switch (idx) {
+    case 0:
+      return f0();
+    case 1:
+      return f1();
+    case 2:
+      return f2();
+    case 3:
+      return f3();
+    case 4:
+      return f4();
+    case 5:
+      return f5();
+    case 6:
+      return f6();
+    case 7:
+      return f7();
+    case 8:
+      return f8();
+    case 9:
+      return f9();
+    case 10:
+      return f10();
+    case 11:
+      return f11();
+    case 12:
+      return f12();
+    case 13:
+      return f13();
+    case 14:
+      return f14();
+    case 15:
+      return f15();
+    case 16:
+      return f16();
+    case 17:
+      return f17();
+    case 18:
+      return f18();
+    case 19:
+      return f19();
+    case 20:
+      return f20();
+  }
+  abort();
+}
+
+template <typename R, typename F0, typename F1, typename F2, typename F3,
+          typename F4, typename F5, typename F6, typename F7, typename F8,
+          typename F9, typename F10, typename F11, typename F12, typename F13,
+          typename F14, typename F15, typename F16, typename F17, typename F18,
+          typename F19, typename F20, typename F21>
+R Switch(char idx, F0 f0, F1 f1, F2 f2, F3 f3, F4 f4, F5 f5, F6 f6, F7 f7,
+         F8 f8, F9 f9, F10 f10, F11 f11, F12 f12, F13 f13, F14 f14, F15 f15,
+         F16 f16, F17 f17, F18 f18, F19 f19, F20 f20, F21 f21) {
+  switch (idx) {
+    case 0:
+      return f0();
+    case 1:
+      return f1();
+    case 2:
+      return f2();
+    case 3:
+      return f3();
+    case 4:
+      return f4();
+    case 5:
+      return f5();
+    case 6:
+      return f6();
+    case 7:
+      return f7();
+    case 8:
+      return f8();
+    case 9:
+      return f9();
+    case 10:
+      return f10();
+    case 11:
+      return f11();
+    case 12:
+      return f12();
+    case 13:
+      return f13();
+    case 14:
+      return f14();
+    case 15:
+      return f15();
+    case 16:
+      return f16();
+    case 17:
+      return f17();
+    case 18:
+      return f18();
+    case 19:
+      return f19();
+    case 20:
+      return f20();
+    case 21:
+      return f21();
+  }
+  abort();
+}
+
+template <typename R, typename F0, typename F1, typename F2, typename F3,
+          typename F4, typename F5, typename F6, typename F7, typename F8,
+          typename F9, typename F10, typename F11, typename F12, typename F13,
+          typename F14, typename F15, typename F16, typename F17, typename F18,
+          typename F19, typename F20, typename F21, typename F22>
+R Switch(char idx, F0 f0, F1 f1, F2 f2, F3 f3, F4 f4, F5 f5, F6 f6, F7 f7,
+         F8 f8, F9 f9, F10 f10, F11 f11, F12 f12, F13 f13, F14 f14, F15 f15,
+         F16 f16, F17 f17, F18 f18, F19 f19, F20 f20, F21 f21, F22 f22) {
+  switch (idx) {
+    case 0:
+      return f0();
+    case 1:
+      return f1();
+    case 2:
+      return f2();
+    case 3:
+      return f3();
+    case 4:
+      return f4();
+    case 5:
+      return f5();
+    case 6:
+      return f6();
+    case 7:
+      return f7();
+    case 8:
+      return f8();
+    case 9:
+      return f9();
+    case 10:
+      return f10();
+    case 11:
+      return f11();
+    case 12:
+      return f12();
+    case 13:
+      return f13();
+    case 14:
+      return f14();
+    case 15:
+      return f15();
+    case 16:
+      return f16();
+    case 17:
+      return f17();
+    case 18:
+      return f18();
+    case 19:
+      return f19();
+    case 20:
+      return f20();
+    case 21:
+      return f21();
+    case 22:
+      return f22();
+  }
+  abort();
+}
+
+template <typename R, typename F0, typename F1, typename F2, typename F3,
+          typename F4, typename F5, typename F6, typename F7, typename F8,
+          typename F9, typename F10, typename F11, typename F12, typename F13,
+          typename F14, typename F15, typename F16, typename F17, typename F18,
+          typename F19, typename F20, typename F21, typename F22, typename F23>
+R Switch(char idx, F0 f0, F1 f1, F2 f2, F3 f3, F4 f4, F5 f5, F6 f6, F7 f7,
+         F8 f8, F9 f9, F10 f10, F11 f11, F12 f12, F13 f13, F14 f14, F15 f15,
+         F16 f16, F17 f17, F18 f18, F19 f19, F20 f20, F21 f21, F22 f22,
+         F23 f23) {
+  switch (idx) {
+    case 0:
+      return f0();
+    case 1:
+      return f1();
+    case 2:
+      return f2();
+    case 3:
+      return f3();
+    case 4:
+      return f4();
+    case 5:
+      return f5();
+    case 6:
+      return f6();
+    case 7:
+      return f7();
+    case 8:
+      return f8();
+    case 9:
+      return f9();
+    case 10:
+      return f10();
+    case 11:
+      return f11();
+    case 12:
+      return f12();
+    case 13:
+      return f13();
+    case 14:
+      return f14();
+    case 15:
+      return f15();
+    case 16:
+      return f16();
+    case 17:
+      return f17();
+    case 18:
+      return f18();
+    case 19:
+      return f19();
+    case 20:
+      return f20();
+    case 21:
+      return f21();
+    case 22:
+      return f22();
+    case 23:
+      return f23();
+  }
+  abort();
+}
+
+template <typename R, typename F0, typename F1, typename F2, typename F3,
+          typename F4, typename F5, typename F6, typename F7, typename F8,
+          typename F9, typename F10, typename F11, typename F12, typename F13,
+          typename F14, typename F15, typename F16, typename F17, typename F18,
+          typename F19, typename F20, typename F21, typename F22, typename F23,
+          typename F24>
+R Switch(char idx, F0 f0, F1 f1, F2 f2, F3 f3, F4 f4, F5 f5, F6 f6, F7 f7,
+         F8 f8, F9 f9, F10 f10, F11 f11, F12 f12, F13 f13, F14 f14, F15 f15,
+         F16 f16, F17 f17, F18 f18, F19 f19, F20 f20, F21 f21, F22 f22, F23 f23,
+         F24 f24) {
+  switch (idx) {
+    case 0:
+      return f0();
+    case 1:
+      return f1();
+    case 2:
+      return f2();
+    case 3:
+      return f3();
+    case 4:
+      return f4();
+    case 5:
+      return f5();
+    case 6:
+      return f6();
+    case 7:
+      return f7();
+    case 8:
+      return f8();
+    case 9:
+      return f9();
+    case 10:
+      return f10();
+    case 11:
+      return f11();
+    case 12:
+      return f12();
+    case 13:
+      return f13();
+    case 14:
+      return f14();
+    case 15:
+      return f15();
+    case 16:
+      return f16();
+    case 17:
+      return f17();
+    case 18:
+      return f18();
+    case 19:
+      return f19();
+    case 20:
+      return f20();
+    case 21:
+      return f21();
+    case 22:
+      return f22();
+    case 23:
+      return f23();
+    case 24:
+      return f24();
+  }
+  abort();
+}
+
+template <typename R, typename F0, typename F1, typename F2, typename F3,
+          typename F4, typename F5, typename F6, typename F7, typename F8,
+          typename F9, typename F10, typename F11, typename F12, typename F13,
+          typename F14, typename F15, typename F16, typename F17, typename F18,
+          typename F19, typename F20, typename F21, typename F22, typename F23,
+          typename F24, typename F25>
+R Switch(char idx, F0 f0, F1 f1, F2 f2, F3 f3, F4 f4, F5 f5, F6 f6, F7 f7,
+         F8 f8, F9 f9, F10 f10, F11 f11, F12 f12, F13 f13, F14 f14, F15 f15,
+         F16 f16, F17 f17, F18 f18, F19 f19, F20 f20, F21 f21, F22 f22, F23 f23,
+         F24 f24, F25 f25) {
+  switch (idx) {
+    case 0:
+      return f0();
+    case 1:
+      return f1();
+    case 2:
+      return f2();
+    case 3:
+      return f3();
+    case 4:
+      return f4();
+    case 5:
+      return f5();
+    case 6:
+      return f6();
+    case 7:
+      return f7();
+    case 8:
+      return f8();
+    case 9:
+      return f9();
+    case 10:
+      return f10();
+    case 11:
+      return f11();
+    case 12:
+      return f12();
+    case 13:
+      return f13();
+    case 14:
+      return f14();
+    case 15:
+      return f15();
+    case 16:
+      return f16();
+    case 17:
+      return f17();
+    case 18:
+      return f18();
+    case 19:
+      return f19();
+    case 20:
+      return f20();
+    case 21:
+      return f21();
+    case 22:
+      return f22();
+    case 23:
+      return f23();
+    case 24:
+      return f24();
+    case 25:
+      return f25();
+  }
+  abort();
+}
+
+template <typename R, typename F0, typename F1, typename F2, typename F3,
+          typename F4, typename F5, typename F6, typename F7, typename F8,
+          typename F9, typename F10, typename F11, typename F12, typename F13,
+          typename F14, typename F15, typename F16, typename F17, typename F18,
+          typename F19, typename F20, typename F21, typename F22, typename F23,
+          typename F24, typename F25, typename F26>
+R Switch(char idx, F0 f0, F1 f1, F2 f2, F3 f3, F4 f4, F5 f5, F6 f6, F7 f7,
+         F8 f8, F9 f9, F10 f10, F11 f11, F12 f12, F13 f13, F14 f14, F15 f15,
+         F16 f16, F17 f17, F18 f18, F19 f19, F20 f20, F21 f21, F22 f22, F23 f23,
+         F24 f24, F25 f25, F26 f26) {
+  switch (idx) {
+    case 0:
+      return f0();
+    case 1:
+      return f1();
+    case 2:
+      return f2();
+    case 3:
+      return f3();
+    case 4:
+      return f4();
+    case 5:
+      return f5();
+    case 6:
+      return f6();
+    case 7:
+      return f7();
+    case 8:
+      return f8();
+    case 9:
+      return f9();
+    case 10:
+      return f10();
+    case 11:
+      return f11();
+    case 12:
+      return f12();
+    case 13:
+      return f13();
+    case 14:
+      return f14();
+    case 15:
+      return f15();
+    case 16:
+      return f16();
+    case 17:
+      return f17();
+    case 18:
+      return f18();
+    case 19:
+      return f19();
+    case 20:
+      return f20();
+    case 21:
+      return f21();
+    case 22:
+      return f22();
+    case 23:
+      return f23();
+    case 24:
+      return f24();
+    case 25:
+      return f25();
+    case 26:
+      return f26();
+  }
+  abort();
+}
+
+template <typename R, typename F0, typename F1, typename F2, typename F3,
+          typename F4, typename F5, typename F6, typename F7, typename F8,
+          typename F9, typename F10, typename F11, typename F12, typename F13,
+          typename F14, typename F15, typename F16, typename F17, typename F18,
+          typename F19, typename F20, typename F21, typename F22, typename F23,
+          typename F24, typename F25, typename F26, typename F27>
+R Switch(char idx, F0 f0, F1 f1, F2 f2, F3 f3, F4 f4, F5 f5, F6 f6, F7 f7,
+         F8 f8, F9 f9, F10 f10, F11 f11, F12 f12, F13 f13, F14 f14, F15 f15,
+         F16 f16, F17 f17, F18 f18, F19 f19, F20 f20, F21 f21, F22 f22, F23 f23,
+         F24 f24, F25 f25, F26 f26, F27 f27) {
+  switch (idx) {
+    case 0:
+      return f0();
+    case 1:
+      return f1();
+    case 2:
+      return f2();
+    case 3:
+      return f3();
+    case 4:
+      return f4();
+    case 5:
+      return f5();
+    case 6:
+      return f6();
+    case 7:
+      return f7();
+    case 8:
+      return f8();
+    case 9:
+      return f9();
+    case 10:
+      return f10();
+    case 11:
+      return f11();
+    case 12:
+      return f12();
+    case 13:
+      return f13();
+    case 14:
+      return f14();
+    case 15:
+      return f15();
+    case 16:
+      return f16();
+    case 17:
+      return f17();
+    case 18:
+      return f18();
+    case 19:
+      return f19();
+    case 20:
+      return f20();
+    case 21:
+      return f21();
+    case 22:
+      return f22();
+    case 23:
+      return f23();
+    case 24:
+      return f24();
+    case 25:
+      return f25();
+    case 26:
+      return f26();
+    case 27:
+      return f27();
+  }
+  abort();
+}
+
+template <typename R, typename F0, typename F1, typename F2, typename F3,
+          typename F4, typename F5, typename F6, typename F7, typename F8,
+          typename F9, typename F10, typename F11, typename F12, typename F13,
+          typename F14, typename F15, typename F16, typename F17, typename F18,
+          typename F19, typename F20, typename F21, typename F22, typename F23,
+          typename F24, typename F25, typename F26, typename F27, typename F28>
+R Switch(char idx, F0 f0, F1 f1, F2 f2, F3 f3, F4 f4, F5 f5, F6 f6, F7 f7,
+         F8 f8, F9 f9, F10 f10, F11 f11, F12 f12, F13 f13, F14 f14, F15 f15,
+         F16 f16, F17 f17, F18 f18, F19 f19, F20 f20, F21 f21, F22 f22, F23 f23,
+         F24 f24, F25 f25, F26 f26, F27 f27, F28 f28) {
+  switch (idx) {
+    case 0:
+      return f0();
+    case 1:
+      return f1();
+    case 2:
+      return f2();
+    case 3:
+      return f3();
+    case 4:
+      return f4();
+    case 5:
+      return f5();
+    case 6:
+      return f6();
+    case 7:
+      return f7();
+    case 8:
+      return f8();
+    case 9:
+      return f9();
+    case 10:
+      return f10();
+    case 11:
+      return f11();
+    case 12:
+      return f12();
+    case 13:
+      return f13();
+    case 14:
+      return f14();
+    case 15:
+      return f15();
+    case 16:
+      return f16();
+    case 17:
+      return f17();
+    case 18:
+      return f18();
+    case 19:
+      return f19();
+    case 20:
+      return f20();
+    case 21:
+      return f21();
+    case 22:
+      return f22();
+    case 23:
+      return f23();
+    case 24:
+      return f24();
+    case 25:
+      return f25();
+    case 26:
+      return f26();
+    case 27:
+      return f27();
+    case 28:
+      return f28();
+  }
+  abort();
+}
+
+template <typename R, typename F0, typename F1, typename F2, typename F3,
+          typename F4, typename F5, typename F6, typename F7, typename F8,
+          typename F9, typename F10, typename F11, typename F12, typename F13,
+          typename F14, typename F15, typename F16, typename F17, typename F18,
+          typename F19, typename F20, typename F21, typename F22, typename F23,
+          typename F24, typename F25, typename F26, typename F27, typename F28,
+          typename F29>
+R Switch(char idx, F0 f0, F1 f1, F2 f2, F3 f3, F4 f4, F5 f5, F6 f6, F7 f7,
+         F8 f8, F9 f9, F10 f10, F11 f11, F12 f12, F13 f13, F14 f14, F15 f15,
+         F16 f16, F17 f17, F18 f18, F19 f19, F20 f20, F21 f21, F22 f22, F23 f23,
+         F24 f24, F25 f25, F26 f26, F27 f27, F28 f28, F29 f29) {
+  switch (idx) {
+    case 0:
+      return f0();
+    case 1:
+      return f1();
+    case 2:
+      return f2();
+    case 3:
+      return f3();
+    case 4:
+      return f4();
+    case 5:
+      return f5();
+    case 6:
+      return f6();
+    case 7:
+      return f7();
+    case 8:
+      return f8();
+    case 9:
+      return f9();
+    case 10:
+      return f10();
+    case 11:
+      return f11();
+    case 12:
+      return f12();
+    case 13:
+      return f13();
+    case 14:
+      return f14();
+    case 15:
+      return f15();
+    case 16:
+      return f16();
+    case 17:
+      return f17();
+    case 18:
+      return f18();
+    case 19:
+      return f19();
+    case 20:
+      return f20();
+    case 21:
+      return f21();
+    case 22:
+      return f22();
+    case 23:
+      return f23();
+    case 24:
+      return f24();
+    case 25:
+      return f25();
+    case 26:
+      return f26();
+    case 27:
+      return f27();
+    case 28:
+      return f28();
+    case 29:
+      return f29();
+  }
+  abort();
+}
+
+template <typename R, typename F0, typename F1, typename F2, typename F3,
+          typename F4, typename F5, typename F6, typename F7, typename F8,
+          typename F9, typename F10, typename F11, typename F12, typename F13,
+          typename F14, typename F15, typename F16, typename F17, typename F18,
+          typename F19, typename F20, typename F21, typename F22, typename F23,
+          typename F24, typename F25, typename F26, typename F27, typename F28,
+          typename F29, typename F30>
+R Switch(char idx, F0 f0, F1 f1, F2 f2, F3 f3, F4 f4, F5 f5, F6 f6, F7 f7,
+         F8 f8, F9 f9, F10 f10, F11 f11, F12 f12, F13 f13, F14 f14, F15 f15,
+         F16 f16, F17 f17, F18 f18, F19 f19, F20 f20, F21 f21, F22 f22, F23 f23,
+         F24 f24, F25 f25, F26 f26, F27 f27, F28 f28, F29 f29, F30 f30) {
+  switch (idx) {
+    case 0:
+      return f0();
+    case 1:
+      return f1();
+    case 2:
+      return f2();
+    case 3:
+      return f3();
+    case 4:
+      return f4();
+    case 5:
+      return f5();
+    case 6:
+      return f6();
+    case 7:
+      return f7();
+    case 8:
+      return f8();
+    case 9:
+      return f9();
+    case 10:
+      return f10();
+    case 11:
+      return f11();
+    case 12:
+      return f12();
+    case 13:
+      return f13();
+    case 14:
+      return f14();
+    case 15:
+      return f15();
+    case 16:
+      return f16();
+    case 17:
+      return f17();
+    case 18:
+      return f18();
+    case 19:
+      return f19();
+    case 20:
+      return f20();
+    case 21:
+      return f21();
+    case 22:
+      return f22();
+    case 23:
+      return f23();
+    case 24:
+      return f24();
+    case 25:
+      return f25();
+    case 26:
+      return f26();
+    case 27:
+      return f27();
+    case 28:
+      return f28();
+    case 29:
+      return f29();
+    case 30:
+      return f30();
+  }
+  abort();
+}
+
+template <typename R, typename F0, typename F1, typename F2, typename F3,
+          typename F4, typename F5, typename F6, typename F7, typename F8,
+          typename F9, typename F10, typename F11, typename F12, typename F13,
+          typename F14, typename F15, typename F16, typename F17, typename F18,
+          typename F19, typename F20, typename F21, typename F22, typename F23,
+          typename F24, typename F25, typename F26, typename F27, typename F28,
+          typename F29, typename F30, typename F31>
+R Switch(char idx, F0 f0, F1 f1, F2 f2, F3 f3, F4 f4, F5 f5, F6 f6, F7 f7,
+         F8 f8, F9 f9, F10 f10, F11 f11, F12 f12, F13 f13, F14 f14, F15 f15,
+         F16 f16, F17 f17, F18 f18, F19 f19, F20 f20, F21 f21, F22 f22, F23 f23,
+         F24 f24, F25 f25, F26 f26, F27 f27, F28 f28, F29 f29, F30 f30,
+         F31 f31) {
+  switch (idx) {
+    case 0:
+      return f0();
+    case 1:
+      return f1();
+    case 2:
+      return f2();
+    case 3:
+      return f3();
+    case 4:
+      return f4();
+    case 5:
+      return f5();
+    case 6:
+      return f6();
+    case 7:
+      return f7();
+    case 8:
+      return f8();
+    case 9:
+      return f9();
+    case 10:
+      return f10();
+    case 11:
+      return f11();
+    case 12:
+      return f12();
+    case 13:
+      return f13();
+    case 14:
+      return f14();
+    case 15:
+      return f15();
+    case 16:
+      return f16();
+    case 17:
+      return f17();
+    case 18:
+      return f18();
+    case 19:
+      return f19();
+    case 20:
+      return f20();
+    case 21:
+      return f21();
+    case 22:
+      return f22();
+    case 23:
+      return f23();
+    case 24:
+      return f24();
+    case 25:
+      return f25();
+    case 26:
+      return f26();
+    case 27:
+      return f27();
+    case 28:
+      return f28();
+    case 29:
+      return f29();
+    case 30:
+      return f30();
+    case 31:
+      return f31();
+  }
+  abort();
+}
+
+}  // namespace grpc_core
+
+#endif  // GRPC_CORE_LIB_PROMISE_DETAIL_SWITCH_H
diff --git a/tools/codegen/core/gen_switch.py b/tools/codegen/core/gen_switch.py
new file mode 100755
index 00000000000..6667959aec3
--- /dev/null
+++ b/tools/codegen/core/gen_switch.py
@@ -0,0 +1,75 @@
+#!/usr/bin/env python3
+
+# Copyright 2021 gRPC authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import sys
+
+
+# utility: print a big comment block into a set of files
+def put_banner(files, banner):
+    for f in files:
+        print('/*', file=f)
+        for line in banner:
+            print(' * %s' % line, file=f)
+        print(' */', file=f)
+        print('', file=f)
+
+
+with open('src/core/lib/promise/detail/switch.h', 'w') as H:
+    # copy-paste copyright notice from this file
+    with open(sys.argv[0]) as my_source:
+        copyright = []
+        for line in my_source:
+            if line[0] != '#':
+                break
+        for line in my_source:
+            if line[0] == '#':
+                copyright.append(line)
+                break
+        for line in my_source:
+            if line[0] != '#':
+                break
+            copyright.append(line)
+        put_banner([H], [line[2:].rstrip() for line in copyright])
+
+    put_banner([H], ["Automatically generated by %s" % sys.argv[0]])
+
+    print("#ifndef GRPC_CORE_LIB_PROMISE_DETAIL_SWITCH_H", file=H)
+    print("#define GRPC_CORE_LIB_PROMISE_DETAIL_SWITCH_H", file=H)
+    print('', file=H)
+    print('#include <grpc/impl/codegen/port_platform.h>', file=H)
+    print('', file=H)
+    print("#include <stdlib.h>", file=H)
+    print('', file=H)
+    print("namespace grpc_core {", file=H)
+
+    for n in range(1, 33):
+        print('', file=H)
+        print("template <typename R, %s> R Switch(char idx, %s) {" % (
+            ", ".join("typename F%d" % i for i in range(0, n)),
+            ", ".join("F%d f%d" % (i, i) for i in range(0, n)),
+        ),
+              file=H)
+        print("  switch (idx) {", file=H)
+        for i in range(0, n):
+            print("   case %d: return f%d();" % (i, i), file=H)
+        print("  }", file=H)
+        print("  abort();", file=H)
+        print("}", file=H)
+
+    print('', file=H)
+    print("}", file=H)
+    print('', file=H)
+    print("#endif // GRPC_CORE_LIB_PROMISE_DETAIL_SWITCH_H", file=H)