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This is a little class template that just builds an inheritance chain of empty classes. Despite how simple this is, it can be used to really nicely create ranked overload sets. I've added a unittest as much to document this as test it. You can pass an object of this type as an argument to a function overload set an it will call the first viable and enabled candidate at or below the rank of the object. I'm planning to use this in a subsequent commit to more clearly rank overload candidates used for SFINAE. All credit for this technique and both lines of code here to Richard Smith who was helping me rewrite the SFINAE check in question to much more effectively capture the intended set of checks. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@279197 91177308-0d34-0410-b5e6-96231b3b80d8
41 lines
1.0 KiB
C++
41 lines
1.0 KiB
C++
//===- STLExtrasTest.cpp - Unit tests for STL extras ----------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/ADT/STLExtras.h"
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#include "gtest/gtest.h"
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using namespace llvm;
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namespace {
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int f(rank<0>) { return 0; }
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int f(rank<1>) { return 1; }
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int f(rank<2>) { return 2; }
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int f(rank<4>) { return 4; }
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TEST(STLExtrasTest, Rank) {
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// We shouldn't get ambiguities and should select the overload of the same
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// rank as the argument.
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EXPECT_EQ(0, f(rank<0>()));
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EXPECT_EQ(1, f(rank<1>()));
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EXPECT_EQ(2, f(rank<2>()));
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// This overload is missing so we end up back at 2.
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EXPECT_EQ(2, f(rank<3>()));
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// But going past 3 should work fine.
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EXPECT_EQ(4, f(rank<4>()));
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// And we can even go higher and just fall back to the last overload.
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EXPECT_EQ(4, f(rank<5>()));
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EXPECT_EQ(4, f(rank<6>()));
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}
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}
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