Feature Proposals » VAR{...boolean="on"...} and ISTRUE{...}

Motivation

There are cases where you want to determine if a preference variable is true or not for sure and safely.

Determining whether a preference is true or not is tricky. You can check if %FOO_ENABLE% is "on" or not by %IF{"$'FOO_ENABLE' = 'on'" ...}%. But ...

• A user may put extra space after "* Set FOO_ENABLE = on", which sets "on " rather than "on" to FOO_NEABLE, in which case the condition "$'FOO_ENABLE' = 'on'" isn't met
• A user may set "1" rather than "on" meaning true

Description and Documentation

A new parameter boolean will be introduced to the VAR variable. The parameter's value is evaluated by TWiki::isTrue(). If it's true, the Boolean mode is turned on. In the Boolean mode, the specified variable's value is handed to TWiki::isTrue(), whose result becomes the result of the %VAR{...}%. TWiki::isTrue() returning either 0 or 1, %VAR{...}% in the Boolean mode results in 0 or 1.

For example, if FOO_ENABLE is set to "off", %VAR{"FOO_ENABLE" boolean="on"}% will be expanded to 0.

%VAR{...boolean="on"...}% is rather verbose considering it will be used often. So a new variable %ISTRUE{...}% will be introduced as a shorthand of %VAR{...boolean="on"}%. %ISTRUE{FOO_ENABLE}% is equivalent to %VAR{"FOO_ENABLE" boolean="on"}%.

There might be cases where you want to specify true and false value. In that case, you will specify false and true values separated by comma.

Examples

%VAR{"FOO_ENABLE" boolean="false,true"}% will be expanded either false or true depending on the value of %FOO_DISABLED%. %ISTRUE{"FOO_ENABLE" boolean="false,true"}% will also work but the former looks better.

%ISTRUE{...}% will be handy in %IF{...}%. e.g. %IF{"%ISTRUE{FOO_ENABLE}%" then="..." else="..."}%.

Impact

Implementation

-- Contributors: Hideyo Imazu - 2014-05-20

Discussion

Looks good!

-- Peter Thoeny - 2014-05-20