c81f4538ec
Summary:
This feature was discussed but not yet proposed. It allows a structured binding to appear as a //condition//
if (auto [ok, val] = f(...))
So the user can save an extra //condition// if the statement can test the value to-be-decomposed instead. Formally, it makes the value of the underlying object of the structured binding declaration also the value of a //condition// that is an initialized declaration.
Considering its logicality which is entirely evident from its trivial implementation, I think it might be acceptable to land it as an extension for now before I write the paper.
Reviewers: rsmith, faisalv, aaron.ballman
Reviewed By: rsmith
Subscribers: aaron.ballman, cfe-commits
Differential Revision: https://reviews.llvm.org/D39284
llvm-svn: 320011
62 lines
1.9 KiB
C++
62 lines
1.9 KiB
C++
// RUN: %clang_cc1 -std=c++1z %s -verify
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struct Na {
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bool flag;
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float data;
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};
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struct Rst {
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bool flag;
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float data;
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explicit operator bool() const {
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return flag;
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}
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};
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Rst f();
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Na g();
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namespace CondInIf {
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void h() {
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if (auto [ok, d] = f()) // expected-warning {{ISO C++17 does not permit structured binding declaration in a condition}}
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;
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if (auto [ok, d] = g()) // expected-warning {{ISO C++17 does not permit structured binding declaration in a condition}} expected-error {{value of type 'Na' is not contextually convertible to 'bool'}}
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;
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}
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} // namespace CondInIf
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namespace CondInWhile {
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void h() {
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while (auto [ok, d] = f()) // expected-warning {{ISO C++17 does not permit structured binding declaration in a condition}}
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;
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while (auto [ok, d] = g()) // expected-warning {{ISO C++17 does not permit structured binding declaration in a condition}} expected-error {{value of type 'Na' is not contextually convertible to 'bool'}}
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;
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}
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} // namespace CondInWhile
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namespace CondInFor {
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void h() {
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for (; auto [ok, d] = f();) // expected-warning {{ISO C++17 does not permit structured binding declaration in a condition}}
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;
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for (; auto [ok, d] = g();) // expected-warning {{ISO C++17 does not permit structured binding declaration in a condition}} expected-error {{value of type 'Na' is not contextually convertible to 'bool'}}
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;
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}
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} // namespace CondInFor
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struct IntegerLike {
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bool flag;
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float data;
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operator int() const {
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return int(data);
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}
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};
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namespace CondInSwitch {
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void h(IntegerLike x) {
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switch (auto [ok, d] = x) // expected-warning {{ISO C++17 does not permit structured binding declaration in a condition}}
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;
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switch (auto [ok, d] = g()) // expected-warning {{ISO C++17 does not permit structured binding declaration in a condition}} expected-error {{statement requires expression of integer type ('Na' invalid)}}
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;
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}
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} // namespace CondInSwitch
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