The reason is directly stated in the Go language spec:
"If the type assertion holds, the value of the expression is the value
stored in x and its type is T. If the type assertion is false, a run-time
panic <https://golang.org/ref/spec#Run_time_panics> occurs."
Here "hold" means if it succeeds.
On Thu, Sep 29, 2016 at 9:53 AM, T L <tapir....@gmail.com> wrote:
>
>
> On Thursday, September 29, 2016 at 12:32:48 PM UTC+8, Henrik Johansson
> wrote:
>>
>> This is just how type assertion works.
>> If you don't use the dual return it panics if the actual type is
>> different from the one you try to assert.
>>
>
> but what is the underlining reason for the inconsistency between map index
> and type assert?
>
>
>>
>> On Thu, Sep 29, 2016, 05:26 T L <tapi...@gmail.com> wrote:
>>
>>> package main
>>>
>>> func main() {
>>> var m = map[string]int{}
>>> _, _ = m["abc"] // ok
>>> _ = m["abc"] // ok
>>>
>>> var i interface{} = 789
>>> _, _ = i.(bool) // ok
>>> _ = i.(bool) // panic: interface conversion: interface is int, not
>>> bool
>>> }
>>>
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