On Friday, February 2, 2018 at 10:45:58 AM UTC-5, Axel Wagner wrote:
>
> From the spec:
>
>
>> If the switch expression evaluates to an untyped constant, it is first
>> converted to its default type; if it is an untyped boolean value, it is
>> first converted to type bool. The predeclared untyped value nil cannot be
>> used as a switch expression.
>
>
> The current behavior is still as specified. Given that there is an
> explicit statement about how this is handled makes it less convincing,
> however, that the spec would be more complicated with a different behavior.
> So you might still file a language change request, if you want.
>
but, why design as such? Isn't untyped bool more convenient?
>
> On Fri, Feb 2, 2018 at 4:39 PM, <di...@veryhaha.com <javascript:>> wrote:
>
>>
>>
>> On Friday, February 2, 2018 at 10:37:24 AM UTC-5, di...@veryhaha.com
>> wrote:
>>
>>>
>>>
>>> On Friday, February 2, 2018 at 10:27:04 AM UTC-5, Ian Lance Taylor wrote:
>>>>
>>>> On Fri, Feb 2, 2018 at 7:10 AM, <di...@veryhaha.com> wrote:
>>>> >
>>>> > Why not make it untyped?
>>>> >
>>>> > package main
>>>> >
>>>> > type T bool
>>>> >
>>>> > func f() T {return T(false)}
>>>> >
>>>> > func main() {
>>>> > switch {
>>>> > case f(): // invalid case f() in switch (mismatched types T and
>>>> bool)
>>>> > }
>>>> > }
>>>>
>>>> The current language spec says that omitting the switch expression is
>>>> equivalent to writing `true`. If you actually write `true`, then,
>>>> following the usual rules for untyped constant expressions, it will
>>>> receive the type `bool`, and you would get the same mismatched type
>>>> error. You will see a similar case if you write `switch 0` and try to
>>>> compare with a named version of `int`. So the compiler is following
>>>> the language spec as currently written.
>>>>
>>>> We could change the language spec to say that omitting the switch
>>>> expression is not equivalent to writing `true`, but instead, as you
>>>> suggest, compares each case to an untyped `true` value. I think the
>>>> main argument against that is that it makes the spec slightly more
>>>> complicated while bringing very little benefit. You could write it up
>>>> as a language change proposal if you like.
>>>>
>>>> Ian
>>>>
>>>
>>> > If you actually write `true`, then,
>>> > following the usual rules for untyped constant expressions,
>>> > it will receive the type `bool`,
>>>
>>> But, in my expression, the result of a constant expression is still
>>> untyped.
>>> And "true" is a per-declared untyped boolean value.
>>>
>>> And, here is another example to should the untyped result is converted
>>> to type "bool":
>>>
>> and sorry again, here "should", I mean "show".
>>
>>
>>>
>>> package main
>>>
>>> type T bool
>>>
>>> func f() T {return T(false)}
>>>
>>> func main() {
>>> switch true == true {
>>> case f(): // invalid case f() in switch (mismatched types T and bool)
>>> }
>>> }
>>>
>>>
>>> --
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>
>
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