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https://github.com/carbon-language/carbon-lang.git
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Jon Ross-Perkins
9134e36ec0
This builds on #5212 which is adding ArgAndKind. This further modifies CARBON_KIND_SWITCH support so that we can use it with ArgAndKind in addition to Inst. That creates a quirk where it's easier if ArgAndKind provides `kind` as an accessor instead of a data member, so I'm just switching it to a class.
96 lines
3.9 KiB
C++
96 lines
3.9 KiB
C++
// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
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// Exceptions. See /LICENSE for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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#ifndef CARBON_TOOLCHAIN_BASE_KIND_SWITCH_H_
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#define CARBON_TOOLCHAIN_BASE_KIND_SWITCH_H_
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#include <type_traits>
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#include "llvm/ADT/STLExtras.h"
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// This library provides switch-like behaviors for Carbon's kind-based types.
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//
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// An expected use case is to mix regular switch `case` statements and
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// `CARBON_KIND`. However, the `switch` must be defined using
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// `CARBON_KIND_SWITCH`. For example:
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//
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// CARBON_KIND_SWITCH(untyped_inst) {
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// case CARBON_KIND(SomeInstType inst): {
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// return inst.typed_field;
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// }
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// case OtherType1::Kind:
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// case OtherType2::Kind:
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// return value;
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// default:
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// return default_value;
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// }
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//
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// For compatibility, this requires:
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//
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// - The type passed to `CARBON_KIND_SWITCH` has `.kind()` to switch on, and
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// `.As<CaseT>` for `CARBON_KIND` to cast to.
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// - Each type passed to `CARBON_KIND` (`CaseT` above) provides
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// `CaseT::Kind`, which is passed to the `case` keyword.
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// `CaseT::Kind::RawEnumType` is the type returned by `.kind()`.
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//
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// Note, this is currently used primarily for Inst in toolchain. When more
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// use-cases are added, it would be worth considering whether the API
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// requirements should change.
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namespace Carbon::Internal::Kind {
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// Given `CARBON_KIND_SWITCH(value)` this returns `value.kind()` to switch on.
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template <typename SwitchT>
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auto SwitchOn(SwitchT&& switch_value) -> auto {
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return switch_value.kind();
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}
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// Given `CARBON_KIND(CaseT name)` this generates `CaseT::Kind`. It explicitly
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// returns `KindT` because that may differ from `CaseT::Kind`, and may not be
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// copyable.
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template <typename SwitchT, typename CaseFnT>
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consteval auto ForCase() -> auto {
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using KindT = llvm::function_traits<
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decltype(&std::remove_cvref_t<SwitchT>::kind)>::result_t;
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using CaseT = llvm::function_traits<CaseFnT>::template arg_t<0>;
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return static_cast<KindT::RawEnumType>(KindT::template For<CaseT>);
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}
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// Given `CARBON_KIND_SWITCH(value)` and `CARBON_KIND(CaseT name)` this
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// generates `value.As<CaseT>()`.
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template <typename FnT, typename ValueT>
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auto Cast(ValueT&& kind_switch_value) -> auto {
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using CaseT = llvm::function_traits<FnT>::template arg_t<0>;
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return kind_switch_value.template As<CaseT>();
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}
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#define CARBON_INTERNAL_KIND_MERGE(Prefix, Line) Prefix##Line
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#define CARBON_INTERNAL_KIND_LABEL(Line) \
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CARBON_INTERNAL_KIND_MERGE(carbon_internal_kind_case_, Line)
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} // namespace Carbon::Internal::Kind
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// Produces a switch statement on value.kind().
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#define CARBON_KIND_SWITCH(value) \
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switch ( \
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const auto& carbon_internal_kind_switch_value = value; \
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::Carbon::Internal::Kind::SwitchOn(carbon_internal_kind_switch_value))
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// Produces a case-compatible block of code that also instantiates a local typed
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// variable. typed_variable_decl looks like `int i`, with a space.
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//
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// This uses `if` to scope the variable, and provides a dangling `else` in order
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// to prevent accidental `else` use. The label allows `:` to follow the macro
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// name, making it look more like a typical `case`.
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#define CARBON_KIND(typed_variable_decl) \
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::Carbon::Internal::Kind::ForCase< \
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decltype(carbon_internal_kind_switch_value), \
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decltype([]([[maybe_unused]] typed_variable_decl) {})>() \
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: if (typed_variable_decl = ::Carbon::Internal::Kind::Cast< \
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decltype([]([[maybe_unused]] typed_variable_decl) {})>( \
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carbon_internal_kind_switch_value); \
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false) {} \
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else [[maybe_unused]] CARBON_INTERNAL_KIND_LABEL(__LINE__)
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#endif // CARBON_TOOLCHAIN_BASE_KIND_SWITCH_H_
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