I do not understand the compiler error when I add the const keyword in the following function which works (and compiles) as expected without the const keyword:

public string getAmountSI(
   in float lnumAmount
   ) const {

   /// (1) given amount

   string lstrAmount;

   if (lnumAmount < 1_000f) {

      lstrAmount = r"1K"c;

   } else {

      if (lnumAmount < 1_000_000f) {

         lstrAmount = format(r"%.0fK"c, lnumAmount / 1_000f);

      } else {

         lstrAmount = format(r"%.0fM"c, lnumAmount / 1_000_000f);

      }

   }

   return lstrAmount;

}

I used to put all attributes BEFORE the function name which now I understand is completely wrong since they should follow the parameter declaration section because putting them before affects the function in other ways.

I first noted this while browsing the DUB package DB and came accross https://code.dlang.org/packages/dscanner which states (among a lot of checks):

• Placement of const, immutable, or inout before a function return type instead of after the parameters

Is it because const for a function is intended to be used ONLY within a structure/class (ie: a method) and thus the this error (http://ddili.org/ders/d.en/const_member_functions.html) ?

Can anyone explain please ?

PS: I think I should re-check all the code I've written so far for things like this that obviously I quite not completely understand yet.

On Wednesday, 30 June 2021 at 17:47:05 UTC, someone wrote:

That is because const/immutable/shared are being applied on the object hence 'this' variable inside function body if function is a member of a struct or class. It doesn't make sense to have a const modifier on a simple function. What will that const mean then in context of that function? To what it will be applied?

Best regards,
alexandri.

On Wednesday, 30 June 2021 at 18:10:52 UTC, Alexandru Ermicioi wrote:

So this will make sense ONLY for an object's method right ?

I think of all the code I have I choose the worst example for asking advice on attribute placement !

Let's use @property instead of const:

struct Foo
{
    @property int data() { return m_data; } // read property

    @property int data(int value) { return m_data = value; } // write property

  private:
    int m_data;
}

In the above example (https://dlang.org/spec/function.html#property-functions) @property is placed before the return type of the property and not after the parameters section.

At first I started to do the same, say, by intuition, but then I saw lots of examples like:

string something() @property { return this.whatever; }

... and changed them accordingly.

Now I am not sure which is the correct way.

Thanks alexandri

On Wednesday, 30 June 2021 at 19:40:40 UTC, someone wrote:

struct Foo
{
    @property int data() { return m_data; } // read property

    @property int data(int value) { return m_data = value; } // write property

  private:
    int m_data;
}

Isn't @property kind of deprecated?

On Thursday, 1 July 2021 at 19:15:50 UTC, Johan Lermer wrote:

The docs state "experimental" not deprecated ... but what this means today I don't know.