If Statement with Declaration
Steven Schveighoffer via Digitalmars-d
digitalmars-d at puremagic.com
Fri Nov 4 07:10:51 PDT 2016
On 11/3/16 6:29 PM, Jerry wrote:
>
> So I was thinking of a way of extending if statements that have
> declarations. The following being as example of the current use of if
> statements with declarations:
>
> if(int* weDontPollute = someFunc())
> {
> // use weDontPollute
> }
>
> That's great and all, but it only works by checking if the variable
> evaluates to true or false. Which is fine for a pointer but otherwise
> useless for anything else, like integers where zero is usually valid
> input (index for array). So currently the only way to do something like
> this in the language, that i've found, is to use a for statement.
>
> for(int i = someFunc(); i >= 0;)
> {
> // use i
>
> break;
> }
>
> Not that ideal to use a for statement. It makes it hard to read and if
> the break condition isn't there it might very well be an infinite loop.
> So I was thinking of some sort of syntax like this:
>
> if(int i = someFunc(); i >= 0)
> {
> // use i
> }
> Thoughts on this sort of feature?
Hm... what about something like:
struct BoolCond(T, string cond)
{
T val;
bool opCast(B)() if(is(B == bool))
{
return mixin("val " ~ cond);
}
}
auto boolcond(string cond, T)(T val)
{
return BoolCond!(T, cond)(val);
}
if(auto i = someFunc.boolcond!(">= 0"))
{
... // use i
}
-Steve
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