Built-ins for booleans - FreeMarker Manual

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# Built-ins for booleans

## c (when used with boolean)

Note:

This built-in exists since FreeMarker 2.3.20.

This built-in converts a boolean to string for a "computer language" as opposed to for human audience. The result will be `"true"` or `"false"`, regardless of the `boolean_format` setting. When generating JavaScript and such, this should be used, as otherwise changing the `boolean_format` can break the generated computer-language output.

Note that this built-in also works on strings.

## string (when used with a boolean value)

All usages of this built-in has been deprecated; see below.

Converts a boolean to a string. You can use it in two ways:

- As `foo?string("yes", "no")`: Deprecated starting from FreeMarker 2.3.23: use `?then("yes", "no")` instead. This will return the first parameter (here: `"yes"`) if the boolean is true, otherwise the second parameter (here: `"no"`). Note that the return value is always a string; if the parameters were numbers, they would be converted to strings first. Also note that both parameters are evaluated, despite that only one of them will be used; this might have negative impact if the parameters aren't just literals.

- `foo?string`: Deprecated starting from FreeMarker 2.3.20: use `?c` instead, or set the `boolean_format` setting to something like `"yes,no"` and then the conversion can happen automatically. If you still need to know about this, this will convert the boolean to string using the default strings for representing true and false values. By default, true is rendered as `"true"` and false is rendered as `"false"`. This is mostly useful if you generate source code with FreeMarker (but use `?c` for that starting from 2.3.20), since the values are not locale (language, country) sensitive. To change these default strings, you can use the `boolean_format` setting.

  Note, that in the very rare case when a value is multi-typed and is both a boolean and a string, then the string value of the variable will be returned, and so the `boolean_format` setting will have no effect.

## then

Note:

This built-in exists since FreeMarker 2.3.23.

Used like `booleanExp?then(whenTrue, whenFalse)`, fills the same role as the ternary operator in C-like languages (i.e., `booleanExp ? whenTrue : whenFalse`). If `booleanExp` evaluates to boolean true then it evaluates and returns its first argument, or else if `booleanExp` evaluates to boolean false then it evaluates and return its second argument. Off course, all three expression can be arbitrary complex. The argument expressions can have any type, even different types.

An important special property of this built-in is that only one of the argument expressions will be evaluated. This is unlike with normal method calls, where all argument expressions are evaluated, regardless if the method will need them. This also means that the argument that's not needed can even refer to missing variables without causing error. (It still can't be syntactically invalid of course.)

Example:

    <#assign foo = true>
    ${foo?then('Y', 'N')}

    <#assign foo = false>
    ${foo?then('Y', 'N')}

    <#assign x = 10>
    <#assign y = 20>
    <#-- Prints 100 plus the maximum of x and y: -->
    ${100 + (x > y)?then(x, y)}

    Y

    N

    120

Note:

If you need to choose based on a non-boolean value, you should use the `switch` built-in instead of nesting multiple `then`-s into each other, like `priority?switch(1, "low", 2, "medium", 3, "high")`, or even `true?switch(priority <= 1, "low", priority == 2, "medium", priority >= 3, "high")`.

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