//===- 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:
/// Trait to check whether `ValueT` provides a 'dyn_cast' method with type
/// `CastT`.
template <typename ValueT, typename CastT>
using has_dyn_cast_t =
decltype(std::declval<ValueT &>().template dyn_cast<CastT>());
/// Attempt to dyn_cast the given `value` to `CastT`. This overload is
/// selected if `value` already has a suitable dyn_cast method.
template <typename CastT, typename ValueT>
static decltype(auto) castValue(
ValueT &&value,
std::enable_if_t<is_detected<has_dyn_cast_t, ValueT, CastT>::value> * =
nullptr) {
return value.template dyn_cast<CastT>();
}
/// Attempt to dyn_cast the given `value` to `CastT`. This overload is
/// selected if llvm::dyn_cast should be used.
template <typename CastT, typename ValueT>
static decltype(auto) castValue(
ValueT &&value,
std::enable_if_t<!is_detected<has_dyn_cast_t, ValueT, CastT>::value> * =
nullptr) {
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