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 //===- TypeSwitch.h - Switch functionality for RTTI casting -*- C++ -*-----===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
 ///  This file implements the TypeSwitch template, which mimics a switch()
 ///  statement whose cases are type names.
 ///
 //===-----------------------------------------------------------------------===/
 
 #ifndef LLVM_ADT_TYPESWITCH_H
 #define LLVM_ADT_TYPESWITCH_H
 
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/Support/Casting.h"
 #include <optional>
 
 namespace llvm {
 namespace detail {
 
 template <typename DerivedT, typename T> class TypeSwitchBase {
 public:
   TypeSwitchBase(const T &value) : value(value) {}
   TypeSwitchBase(TypeSwitchBase &&other) : value(other.value) {}
   ~TypeSwitchBase() = default;
 
   /// TypeSwitchBase is not copyable.
   TypeSwitchBase(const TypeSwitchBase &) = delete;
   void operator=(const TypeSwitchBase &) = delete;
   void operator=(TypeSwitchBase &&other) = delete;
 
   /// Invoke a case on the derived class with multiple case types.
   template <typename CaseT, typename CaseT2, typename... CaseTs,
             typename CallableT>
   // This is marked always_inline and nodebug so it doesn't show up in stack
   // traces at -O0 (or other optimization levels).  Large TypeSwitch's are
   // common, are equivalent to a switch, and don't add any value to stack
   // traces.
   LLVM_ATTRIBUTE_ALWAYS_INLINE LLVM_ATTRIBUTE_NODEBUG DerivedT &
   Case(CallableT &&caseFn) {
     DerivedT &derived = static_cast<DerivedT &>(*this);
     return derived.template Case<CaseT>(caseFn)
         .template Case<CaseT2, CaseTs...>(caseFn);
   }
 
   /// Invoke a case on the derived class, inferring the type of the Case from
   /// the first input of the given callable.
   /// Note: This inference rules for this overload are very simple: strip
   ///       pointers and references.
   template <typename CallableT> DerivedT &Case(CallableT &&caseFn) {
     using Traits = function_traits<std::decay_t<CallableT>>;
     using CaseT = std::remove_cv_t<std::remove_pointer_t<
         std::remove_reference_t<typename Traits::template arg_t<0>>>>;
 
     DerivedT &derived = static_cast<DerivedT &>(*this);
     return derived.template Case<CaseT>(std::forward<CallableT>(caseFn));
   }
 
 protected:
   /// Attempt to dyn_cast the given `value` to `CastT`.
   template <typename CastT, typename ValueT>
   static decltype(auto) castValue(ValueT &&value) {
     return dyn_cast<CastT>(value);
   }
 
   /// The root value we are switching on.
   const T value;
 };
 } // end namespace detail
 
 /// This class implements a switch-like dispatch statement for a value of 'T'
 /// using dyn_cast functionality. Each `Case<T>` takes a callable to be invoked
 /// if the root value isa<T>, the callable is invoked with the result of
 /// dyn_cast<T>() as a parameter.
 ///
 /// Example:
 ///  Operation *op = ...;
 ///  LogicalResult result = TypeSwitch<Operation *, LogicalResult>(op)
 ///    .Case<ConstantOp>([](ConstantOp op) { ... })
 ///    .Default([](Operation *op) { ... });
 ///
 template <typename T, typename ResultT = void>
 class TypeSwitch : public detail::TypeSwitchBase<TypeSwitch<T, ResultT>, T> {
 public:
   using BaseT = detail::TypeSwitchBase<TypeSwitch<T, ResultT>, T>;
   using BaseT::BaseT;
   using BaseT::Case;
   TypeSwitch(TypeSwitch &&other) = default;
 
   /// Add a case on the given type.
   template <typename CaseT, typename CallableT>
   TypeSwitch<T, ResultT> &Case(CallableT &&caseFn) {
     if (result)
       return *this;
 
     // Check to see if CaseT applies to 'value'.
     if (auto caseValue = BaseT::template castValue<CaseT>(this->value))
       result.emplace(caseFn(caseValue));
     return *this;
   }
 
   /// As a default, invoke the given callable within the root value.
   template <typename CallableT>
   [[nodiscard]] ResultT Default(CallableT &&defaultFn) {
     if (result)
       return std::move(*result);
     return defaultFn(this->value);
   }
   /// As a default, return the given value.
   [[nodiscard]] ResultT Default(ResultT defaultResult) {
     if (result)
       return std::move(*result);
     return defaultResult;
   }
 
   [[nodiscard]] operator ResultT() {
     assert(result && "Fell off the end of a type-switch");
     return std::move(*result);
   }
 
 private:
   /// The pointer to the result of this switch statement, once known,
   /// null before that.
   std::optional<ResultT> result;
 };
 
 /// Specialization of TypeSwitch for void returning callables.
 template <typename T>
 class TypeSwitch<T, void>
     : public detail::TypeSwitchBase<TypeSwitch<T, void>, T> {
 public:
   using BaseT = detail::TypeSwitchBase<TypeSwitch<T, void>, T>;
   using BaseT::BaseT;
   using BaseT::Case;
   TypeSwitch(TypeSwitch &&other) = default;
 
   /// Add a case on the given type.
   template <typename CaseT, typename CallableT>
   TypeSwitch<T, void> &Case(CallableT &&caseFn) {
     if (foundMatch)
       return *this;
 
     // Check to see if any of the types apply to 'value'.
     if (auto caseValue = BaseT::template castValue<CaseT>(this->value)) {
       caseFn(caseValue);
       foundMatch = true;
     }
     return *this;
   }
 
   /// As a default, invoke the given callable within the root value.
   template <typename CallableT> void Default(CallableT &&defaultFn) {
     if (!foundMatch)
       defaultFn(this->value);
   }
 
 private:
   /// A flag detailing if we have already found a match.
   bool foundMatch = false;
 };
 } // end namespace llvm
 
 #endif // LLVM_ADT_TYPESWITCH_H

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