Built-ins for booleans

c (when used with boolean)

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 configuration setting, as that setting is meant to specify the format for human consumption. When generating boolean literals for JavaScript and such, this should be used.

If you only generate output that's computer language and isn't read by end-users, you may want to set the boolean_format configuration setting to c (since FreeMarker 2.3.29), in which case ${aBoolean} will have the same output as ${aBoolean?c}.

Note that this built-in also works on strings.

string (when used with a boolean value)

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

• As foo?string("yes", "no"): Formats the boolean value to the first parameter (here: "yes") if the boolean is true, and to the second parameter (here: "no") if it's false. Unless you only meant to format a boolean with simple literals, use ?then(whenTrue, whenFalse) instead, as that has less type limitations, and it evaluate its parameters lazily! The return value of ?string is always a string (unlike for ?then), because if the parameters aren't strings, they will be converted to strings. Also note that both parameters are evaluated (unlike for ?then), despite that only one of them will be used; this might has 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 only useful if you generate source code with FreeMarker (but use ?c for that starting from 2.3.20). 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

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

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