Ternary operator shorthand

[lmcd]

I tend to find myself doing a lot of things like this:
{{ foo ? 'yes' : '' }}

This happens quite often when defining CSS class names. Would it be possible to shorten the code in these instances to:
{{ foo ? 'yes' }}

[markstory]

I don't know if overloading the ? like that is a good idea. This could easily be confused with PHP 5.3's shortcut ternary ?:, or a broken ternary. Perhaps something like {{ condition ?= 'output' }} could work.

[lmcd]

I can't really see how it would cause confusion. I've always read the ternary operator as:
{{ if ? then : else }}
The proposed change just optionally drops the else. So:
{{ if ? then }}

Either way, the '?=' syntax isn't bad either and is still cleaner than the current method.

[elliot]

Would you be looking for the default filter?

eg:
{{ foo | default('yes') }}

[fabpot]

Like eliot said, the default filter is probably the best answer.

[Seldaek]

Nah this has nothing to do with the default filter. {{ foo|default('yes') }} is equivalent to {{ foo ? foo : 'yes'}} or shorthand {{ foo ?: 'yes' }}. What was proposed by lmcd is to be able to drop the "false" case, i.e. {{ foo ? 'yes' : '' }} or shorthand {{ foo ? 'yes' }}.

I think this would be a good change for brevity's sake (which adds readability in cluttered templates), even supporting the {{ foo ?: 'bar' }} wouldn't be bad imo.

[vladcosorg]

So was it implemented?
I find myself constantly dropping the 'else' part, wouldn't it be easier to make implement suggested syntax?

[lmcd]

Still wouldn't mind seeing this implemented either. As @sedaek said, would be a step towards making complicated templates more readable.

[char101]

I think this is more in line with current twig syntax

{{ 'yes' if foo }}

with else

{{ 'yes' if foo else 'no' }}

[fabpot]

@char101 I kinda like this proposal as it reminds me of my good old Perl days ;)

[char101]

@fabpot It's also the syntax used by python. Since twig seems to take inspiration from Jinja, I think it's only natural to add the if expression syntax from python.

[fabpot]

Anyone willing to see if the implementation would be easy or hard? I suspect that it won't be that easy.

[mrxotey]

There is implementation of "if()" filter in Twig-Extensions: twigphp/Twig-extensions#43

I use this filter in my projects.

[char101]

This is an example implementation

protected function parseConditionalExpression($expr)
{
    $ternary = false;
    while ($this->parser->getStream()->test(Twig_Token::PUNCTUATION_TYPE, '?')) {
        $this->parser->getStream()->next();
        $expr2 = $this->parseExpression();
        $this->parser->getStream()->expect(Twig_Token::PUNCTUATION_TYPE, ':', 'The ternary operator must have a default value');
        $expr3 = $this->parseExpression();

        $expr = new Twig_Node_Expression_Conditional($expr, $expr2, $expr3, $this->parser->getCurrentToken()->getLine());
        $ternary = true;
    }

    if (! $ternary) {
        while ($this->parser->getStream()->test(Twig_Token::NAME_TYPE, 'if')) {
            $this->parser->getStream()->next();
            $condition_expr = $this->parseExpression();
            if ($this->parser->getStream()->test(Twig_Token::NAME_TYPE, 'else')) {
                $this->parser->getStream()->next();
                $else_expr = $this->parseExpression();
            } else {
                $else_expr = new Twig_Node_Expression_Constant('', $this->parser->getCurrentToken()->getLine());
            }
            $expr = new Twig_Node_Expression_Conditional($condition_expr, $expr, $else_expr, $this->parser->getCurrentToken()->getLine());
        }
    }

    return $expr;
}

test case

<?php

require_once 'Twig/Autoloader.php';
Twig_Autoloader::register();

$loader = new Twig_Loader_String;
$twig = new Twig_Environment($loader);

echo $twig->render('{{ "Hello" if false else "World" }}');

[char101]

Some test cases

input : 'Hello' if true
output: Hello
input : 'Hello' if false else 'World'
output: World
input : 'Hello' if 1 + 1 > 0
output: Hello
input : 'Hello' if 0 else 'a' ~ 'b'
output: ab
input : 'Hello' if 1 if true
output: Hello
input : 'Hello' if 1 if false else 0
output:
input : 'Hello' if 1 if false else 0 else 'World'
output: World