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Commit 83c6f9ee authored by Lloyd Pique's avatar Lloyd Pique
Browse files

Easier ftl::Flags construction 

As demonstrated by the existing test, while it is possible to construct
a ftl::Flags<E> from multiple values, it requires an extra
`using namespace ftl::flag_operators` or alternatively a
`using ftl::flag_operators::operator|` to implicitly construct a
`ftl::Flags<E>` type.

But there is an easier way -- allow implicit construction from a
`std::initializer_list<E>`.

This means as an alternative to:

    using namespace ftl::flag_operators;
    ftl::Flags<E> x = E::A | E::B;

... one can instead write:

    ftl::Flags<E> x = {E::A, E::B};

... and achieve the same initial value.

This change adds the new constructor overload.

Assignment from an initializer list automatically works, without having
to define a explicit `operator=(std::initializer_list<E>)`. Instead the
copy constuctor is used.

As a useful side effect, you can now also clear the flags by assigning
an empty initializer list:

    ftl::Flags<E> x;
    x = {};  // Clears x to zero

Bug: 185536303
Flag: EXEMPT New library code
Test: atest ftl_test
Change-Id: I1de7857c93ebef4fc5e6157aac9cf162b49943e1
parent 1a824fd3

include/ftl/flags.h

+10 −0
Original line number Diff line number Diff line
@@ -22,6 +22,7 @@ 
#include <bitset>

#include <cstdint>

#include <iterator>

#include <initializer_list>

#include <string>

#include <type_traits>
@@ -40,6 +41,7 @@ class Flags { 


public:

    constexpr Flags(F f) : mFlags(static_cast<U>(f)) {}

    constexpr Flags(std::initializer_list<F> fs) : mFlags(combine(fs)) {}

    constexpr Flags() : mFlags(0) {}

    constexpr Flags(const Flags<F>& f) : mFlags(f.mFlags) {}
@@ -197,6 +199,14 @@ public: 
private:

    U mFlags;



    static constexpr U combine(std::initializer_list<F> fs) {

        U result = 0;

        for (const F f : fs) {

            result |= static_cast<U>(f);

        }

        return result;

    }



    static void appendFlag(std::string& str, const std::string_view& flag, bool& first) {

        if (first) {

            first = false;

libs/ftl/flags_test.cpp

+13 −1
Original line number Diff line number Diff line
@@ -17,7 +17,7 @@ 
#include <ftl/flags.h>

#include <gtest/gtest.h>



#include <type_traits>

#include <initializer_list>



namespace android::test {
@@ -59,6 +59,18 @@ TEST(Flags, All) { 
    ASSERT_FALSE(flags.all(TestFlags::ONE | TestFlags::TWO | TestFlags::THREE));

}



TEST(Flags, ImplicitConstructionAndAssignmentFromInitializerList) {

    Flags<TestFlags> flags = {TestFlags::ONE, TestFlags::THREE};

    ASSERT_TRUE(flags.test(TestFlags::ONE));

    ASSERT_FALSE(flags.test(TestFlags::TWO));

    ASSERT_TRUE(flags.test(TestFlags::THREE));



    flags = {};

    ASSERT_FALSE(flags.test(TestFlags::ONE));

    ASSERT_FALSE(flags.test(TestFlags::TWO));

    ASSERT_FALSE(flags.test(TestFlags::THREE));

}



TEST(Flags, DefaultConstructor_hasNoFlagsSet) {

    Flags<TestFlags> flags;

    ASSERT_FALSE(flags.any(TestFlags::ONE | TestFlags::TWO | TestFlags::THREE));