Let's say that I'm a library provider and I intend to offer a completely new data type suitable for printing with format() or writef().

According to this tutorial (http://wiki.dlang.org/Defining_custom_print_format_specifiers), to achieve this, one must import at least std.format : FormatSpec.

The problem is that just importing FormatSpec will create exactly 88 phobos dependencies.

Is there any way to provide formatting capabilities for a custom data type without importing the FormatSpec thing?

On Mon, Nov 09, 2015 at 03:09:26PM +0000, rumbu via Digitalmars-d-learn wrote:
> Let's say that I'm a library provider and I intend to offer a
> completely new data type suitable for printing with format() or
> writef().
> 
> According to this tutorial (http://wiki.dlang.org/Defining_custom_print_format_specifiers), to achieve this, one must import at least std.format : FormatSpec.
> 
> The problem is that just importing FormatSpec will create exactly 88 phobos dependencies.
> 
> Is there any way to provide formatting capabilities for a custom data type without importing the FormatSpec thing?

Do you need *custom* format specifiers? If all you need is to be able to write: format("%s", myData), then the only thing you need to do is to implement one of the toString methods recognized by format(), such as:

	void toString(scope void delegate(const(char)[]) dg) {
		...
	}

and format() should be able to just pick it up.


T

-- 
You have to expect the unexpected. -- RL

On Monday, 9 November 2015 at 16:11:23 UTC, H. S. Teoh wrote:
> On Mon, Nov 09, 2015 at 03:09:26PM +0000, rumbu via Digitalmars-d-learn wrote:
>> [...]
>
> Do you need *custom* format specifiers? If all you need is to be able to write: format("%s", myData), then the only thing you need to do is to implement one of the toString methods recognized by format(), such as:
>
> 	void toString(scope void delegate(const(char)[]) dg) {
> 		...
> 	}
>
> and format() should be able to just pick it up.
>
>
> T
I'm working to create a decimal data type library, therefore I need at least %f %e %a and %g, including other data like width, precision and so on.

On Monday, 9 November 2015 at 15:09:28 UTC, rumbu wrote:
> The problem is that just importing FormatSpec will create exactly 88 phobos dependencies.

I would pull request that to move it into its own independent module and then make std.format import that. I know that's not an immediate solution but it should go through by the next release; i doubt such a PR would be controversial.