返回值指针语法

Question

In the following code:

type boolValue bool

func newBoolValue(val bool, p *bool) *boolValue {
    *p = val
    return (*boolValue)(p)
}

What is the last line doing?

Answer 1

The Go Programming Language Specification

Conversions

Conversions are expressions of the form T(x) where T is a type and x is an expression that can be converted to type T.

type boolValue bool

func newBoolValue(val bool, p *bool) *boolValue {
    *p = val
    return (*boolValue)(p)
}

(*boolValue)(p) is doing a type conversion from *bool, the type of p, to *boolValue, the type of the newBoolValue function return value. Go requires explicit conversions. The conversion is allowed because bool is the underlying type of boolValue.

If you simply write return p without the conversion the compiler error message explains the problem:

return p

error: cannot use p (type *bool) as type *boolValue in return argument