vibe.d selectively include attribute into tag using diet template

[JG via Digitalmars-d-learn]

Hi,

I know that one can do the following:
tag(attribute='#{dexpression}')

But, is there a way to deal with attributes that don't get 
assigned values.

That is, is there a way to produce

or

depending on a boolean variable?

Of course one can do:
- if (booleanVariable)
 tag(attribute)
  include ...
- if (!booleanVariable)
 tag
  include ...

But this seems rather messy.

Re: vibe.d selectively include attribute into tag using diet template

[Steven Schveighoffer via Digitalmars-d-learn]

On 2/27/21 12:48 PM, JG wrote:

Hi,

I know that one can do the following:
tag(attribute='#{dexpression}')

But, is there a way to deal with attributes that don't get assigned values.
That is, is there a way to produce

or

depending on a boolean variable?

Of course one can do:
- if (booleanVariable)
  tag(attribute)
   include ...
- if (!booleanVariable)
  tag
   include ...

But this seems rather messy.


Yes, if you assign a boolean value to it directly, then if true, the 
attribute is included, if not, it's not.


e.g.:

tag(attribute=booleanVariable)

Note the lack of quotes. If you us an expression without quotes in diet, 
it becomes an interpolation. In the special case that it's a boolean, it 
becomes a switch to tell whether to include the attribute or not. If 
it's a complex expression you might need parentheses:


tag(attribute=(booleanVariable ? true : false))

-Steve

Re: vibe.d selectively include attribute into tag using diet template

[JG via Digitalmars-d-learn]

On Saturday, 27 February 2021 at 19:12:55 UTC, Steven 
Schveighoffer wrote:


Yes, if you assign a boolean value to it directly, then if 
true, the attribute is included, if not, it's not.


e.g.:

tag(attribute=booleanVariable)

Note the lack of quotes.


Thank you very much for this.


If you use an expression without quotes
in diet, it becomes an interpolation.


Would you mind explaining in more detail what this means? How 
could one use this, other than with booleans?

How can I make this work?

[Jack via Digitalmars-d-learn]

I'm using a windows callback function where the user-defined 
value is passed thought a LPARAM argument type. I'd like to pass 
my D array then access it from that callback function. How is the 
casting from LPARAM to my type array done in that case?


for example, I need something like this to work:

int[] arr = [1, 2, 3];
long l = cast(long) cast(void*) arr.ptr;
int[] a = cast(int[]) cast(void*) l;

Re: How can I make this work?

[evilrat via Digitalmars-d-learn]

On Sunday, 28 February 2021 at 07:05:27 UTC, Jack wrote:
I'm using a windows callback function where the user-defined 
value is passed thought a LPARAM argument type. I'd like to 
pass my D array then access it from that callback function. How 
is the casting from LPARAM to my type array done in that case?


for example, I need something like this to work:

int[] arr = [1, 2, 3];
long l = cast(long) cast(void*) arr.ptr;
int[] a = cast(int[]) cast(void*) l;


Should already work like that. Just be aware that array can be 
garbage collected if no references for it are kept somewhere else 
between set callback and the actual call, otherwise you can get 
some random garbage.


Also be aware that such casts 99% basically a speculation, there 
is no guarantee that returned data is actually an int[].