Assignability of function parameters in golang

Question

type Boolean bool

func takes_bool(b bool) {
    fmt.Printf("%t\n", b)
}

func takes_boolean(b Boolean) {
    fmt.Printf("%t\n", b)
}

When I invoke the following:

takes_bool(Boolean(false))
takes_bool(Boolean(true))

I get:

cannot use Boolean(false) (type Boolean) as type bool in function argument
cannot use Boolean(true) (type Boolean) as type bool in function argument

The rules on assignability seems to NOT disallow it i.e. at least one is not a named type & both have the same underlying type:

type Boolean bool

vs

bool

Evan · Accepted Answer · 2014-04-08 21:23:29Z

2

On a careful reading of http://golang.org/ref/spec#Types it seems bool is considered a named type (as are int and float and friends). The phrase "unnamed types" only refer to type literals like interface{} and struct{}.

answered Apr 8, 2014 at 21:23

Evan

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2 Comments

canadadry Over a year ago

function takes_boolean can accept both bare true and false. So now you have 2 named types.

Evan Over a year ago

bool and Boolean are both named types. However, bareword true and false are untyped constant literals, falling under the last bullet point in golang.org/ref/spec#Assignability See also golang.org/ref/spec#Constants

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