[Pas2js] Built-in helper methods for Double type

[Sven Barth]

Am 04.09.2019 um 23:25 schrieb Mattias Gaertner via Pas2js:
> On Wed, 4 Sep 2019 11:26:42 -0700 (MST)
> warleyalex via Pas2js <pas2js at lists.freepascal.org> wrote:
>
>> solution using type helpers:
>> ==================
>> type
>>    Float = Double;
>>
>> type
>> { TDoubleHelper }
>> TDoubleHelper = type helper for Float
>>     function toFixed(aNumber: Double; fractionDigits: integer): string;
>> assembler;
>> end;
>>
>> { TDoubleHelper }
>> function TDoubleHelper.toFixed(aNumber: Double; fractionDigits:
>> integer): string; assembler;
>> asm
>>    return Number(aNumber).toFixed(fractionDigits);
>> end;
>>
>>
>> var
>>    ReturnValue: float;
>>    x: String;
>> begin
>>    x := ReturnValue.toFixed(sin(10.1) * 2.5, 2);
>>
>>    rtl.createHelper($mod,"TDoubleHelper",null,function () {
>>      this.toFixed = function (aNumber, fractionDigits) {
>>        return Number(aNumber).toFixed(fractionDigits);
>>      };
>>    });
>>
>>     $mod.x = $mod.TDoubleHelper.toFixed.call({p: $mod, get: function
>> () { return this.p.ReturnValue;
>>       }, set: function (v) {
>>         this.p.ReturnValue = v;
>>       }},Math.sin(10.1) * 2.5,2);
>>
>>
>> Personaly, I don't like being able to specify a type helper, jsut
>> because Class helpers are not attractive. It's a kind of weird
>> thing :)
>>
>> I just want to determine X and cut to 2 decimals, using type helper,
>> this weird syntax:
>>
>>    x := ReturnValue.toFixed(sin(rad) * r, 2); // type helpers it's
>> weird and generates extra code
> Delphi defines type helpers as pass value by reference - a type helper
> can modify the value. That's why pas2js must for compatibility
> reasons create this weird awkward code.
> Iff there would be a modifier or attribute to define a read only type
> helper method, the compiler could create shorter code.

Considering that Delphi is using attributes for most such things as well 
(WeakRef, Volatile, etc.) you could add a magic "SelfIsConstAttribute" 
or something like that...

> Another possibility would be a whole program analysis to spot if a
> type helper method is read-only and never referenced via address. But
> that would only work for Pascal methods, not external ones.
Couldn't external ones be considered as "const" anyway? Or can JS code 
modify "this"?

Regards,
Sven