readability-implicit-bool-conversion¶
This check can be used to find implicit conversions between built-in types and booleans. Depending on use case, it may simply help with readability of the code, or in some cases, point to potential bugs which remain unnoticed due to implicit conversions.
The following is a real-world example of bug which was hiding behind implicit
bool
conversion:
class Foo {
int m_foo;
public:
void setFoo(bool foo) { m_foo = foo; } // warning: implicit conversion bool -> int
int getFoo() { return m_foo; }
};
void use(Foo& foo) {
bool value = foo.getFoo(); // warning: implicit conversion int -> bool
}
This code is the result of unsuccessful refactoring, where type of m_foo
changed from bool
to int
. The programmer forgot to change all
occurrences of bool
, and the remaining code is no longer correct, yet it
still compiles without any visible warnings.
In addition to issuing warnings, fix-it hints are provided to help solve the reported issues. This can be used for improving readability of code, for example:
void conversionsToBool() {
float floating;
bool boolean = floating;
// ^ propose replacement: bool boolean = floating != 0.0f;
int integer;
if (integer) {}
// ^ propose replacement: if (integer != 0) {}
int* pointer;
if (!pointer) {}
// ^ propose replacement: if (pointer == nullptr) {}
while (1) {}
// ^ propose replacement: while (true) {}
}
void functionTakingInt(int param);
void conversionsFromBool() {
bool boolean;
functionTakingInt(boolean);
// ^ propose replacement: functionTakingInt(static_cast<int>(boolean));
functionTakingInt(true);
// ^ propose replacement: functionTakingInt(1);
}
In general, the following conversion types are checked:
- integer expression/literal to boolean (conversion from a single bit bitfield to boolean is explicitly allowed, since there’s no ambiguity / information loss in this case),
- floating expression/literal to boolean,
- pointer/pointer to member/
nullptr
/NULL
to boolean, - boolean expression/literal to integer (conversion from boolean to a single bit bitfield is explicitly allowed),
- boolean expression/literal to floating.
The rules for generating fix-it hints are:
- in case of conversions from other built-in type to bool, an explicit
comparison is proposed to make it clear what exactly is being compared:
bool boolean = floating;
is changed tobool boolean = floating == 0.0f;
,- for other types, appropriate literals are used (
0
,0u
,0.0f
,0.0
,nullptr
),
- in case of negated expressions conversion to bool, the proposed replacement
with comparison is simplified:
if (!pointer)
is changed toif (pointer == nullptr)
,
- in case of conversions from bool to other built-in types, an explicit
static_cast
is proposed to make it clear that a conversion is taking place:int integer = boolean;
is changed toint integer = static_cast<int>(boolean);
,
- if the conversion is performed on type literals, an equivalent literal is
proposed, according to what type is actually expected, for example:
functionTakingBool(0);
is changed tofunctionTakingBool(false);
,functionTakingInt(true);
is changed tofunctionTakingInt(1);
,- for other types, appropriate literals are used (
false
,true
,0
,1
,0u
,1u
,0.0f
,1.0f
,0.0
,1.0f
).
Some additional accommodations are made for pre-C++11 dialects:
false
literal conversion to pointer is detected,- instead of
nullptr
literal,0
is proposed as replacement.
Occurrences of implicit conversions inside macros and template instantiations are deliberately ignored, as it is not clear how to deal with such cases.