Question about: ("1.1").to!int;

matheus matheus at
Fri Oct 23 16:59:06 UTC 2020

On Friday, 23 October 2020 at 13:57:41 UTC, Joseph Rushton 
Wakeling wrote:
> On Wednesday, 21 October 2020 at 22:50:27 UTC, matheus wrote:
>> Since (1.1).to!int = 1, shouldn't the string value 
>> ("1.1").to!int at least try to convert to float/double and 
>> then to int?
> The thing is, that's a great way for hard-to-identify bugs to 
> creep into code.  In these cases:
>     auto a = (1).to!int;     // this works
>     auto b = ("1").to!int;   // this works
>     auto c = (1.1).to!int;   // this works and c = 1
> ... then what the programmer wants is unambiguous.  In the 
> first case it's just converting int => int.  In the second, 
> it's converting from a string that unambiguously represents an 
> integer value, to an int.  And in the third, it's converting 
> _at programmer request_ from a double to an int (which has a 
> well-defined behaviour).
> However, if ("1.1").to!int were to work, this would be the `to` 
> function making a judgement call on how to handle something 
> ambiguous.  And while that judgement call may be acceptable for 
> your current use-case, it won't be for others.

I got it everything you said, but like a said previously:

(1.1).to!int vs ("1.1").to!int

One is a decimal literal while the other is a string 
representation of a decimal.

To be honest I think the function is already making a judgment 
call when I do (1.1).to!int and returns 1, I really fail to see 
the difference when is ("1.1").to!int.

I agree with user1234: "The third case is just like `cast(int) 
1.1` it's not _at programmer request_ from my point of view, it's 
just that the `to` template has not be more restrictive than the 
D `cast` expression. `to` should do at least what a `cast` do and 
do more when there's no rule for the two types that are involved."

> In particular, if `to` just accepted any string numerical 
> representation for conversion to int, how could the caller 
> explicitly _exclude_ non-integer input, if that is their 
> use-case?

Well since the caller is handling a string, shouldn't the caller 
verify the content before any conversion?

Because a string may contain a integer, decimal representation or 
neither one.

Finally I don't want to make a fuss of it, I just thought it was 
a bit weird but it can be solved easily.



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