Automatic typing

[JS]

On Monday, 1 July 2013 at 01:56:22 UTC, Timon Gehr wrote:
> On 07/01/2013 03:08 AM, Kenji Hara wrote:
>> 2013/7/1 JS <js.mdnq at gmail.com <mailto:js.mdnq at gmail.com>>
>>
>>    I am simply talking about having the compiler enlarge the 
>> type if
>>    needed. (this is mainly for built in types since the type 
>> hierarchy
>>    is explicitly known)
>>
>>
>> Just a simple matter, it would *drastically* increase 
>> compilation time.
>>
>> void foo()
>> {
>>     auto elem;
>>     auto arr = [elem];
>>
>>     elem = 1;
>>     ....
>>     elem = 2.0;
>>     // typeof(elem) change should modify the result of 
>> typeof(arr)
>> }
>>
>> Such type dependencies between multiple variables are common 
>> in the
>> realistic program.
>>
>> When `elem = 2.0;` is found, compiler should run semantic 
>> analysis of
>> the whole function body of foo _once again_, because the 
>> setting type of
>> elem ignites the change of typeof(arr), and it would affect 
>> the code
>> meaning.
>>
>> If another variable type would be modified, it also ignites 
>> the whole
>> function body semantic again.
>>
>> After all, semantic analysis repetition would drastically 
>> increase.
>>
>> I can easily imagine that the compilation cost would not be 
>> worth the
>> small benefits.
>>
>> Kenji Hara
>
> The described strategy can easily result in non-termination, 
> and which template instantiations it performs can be 
> non-obvious.
>
> auto foo(T)(T arg){
>     static if(is(T==int)) return 1.0;
>     else return 1;
> }
>
> void main(){
>     auto x;
>     x = 1;
>     x = foo(x);
> }

Sorry, it only results in non-termination if you don't check all 
return types out of a function. It is a rather easy case to 
handle by just following all the return types and choosing the 
largest one. No big deal...  any other tries?