5.7. New data formats
5.7.1. Variables
5.7. New data formats
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5.7.1. Variables

In this chapter, we are going to learn, how to change the behavior of variables with OPT data formats.

Configuration

The variable access snippets are located in the variable group, so you must add it to $_supports field in your data format. Furthermore, you need to set up the property variable:assign. It is a boolean value that controls whether your data format supports assignments of a new value to the variables. Another property is variable:useReference. Its value should be true if the data format permits reading the variables via references. For example, the data format shown in the example below that implements the template variables as functions, should use false here, as it is not possible in PHP to access the returned function values via references.

Reading the values

The snippet that returns the PHP code to read a variable value is called variable:main. It should return a piece of expression that reads the value. The variable name is provided in the item format variable.

    case 'variable:main':
        return 'myVariableReader(\''.$this->_getVar('item').'\')';

OPT supports both local and global template variables. The data formats may return different PHP codes for those two types of variables. The requested type is provided in the access format variable which takes two possible values:

  1. Opt_Class::ACCESS_LOCAL - accessing a local variable
  2. Opt_Class::ACCESS_GLOBAL - accessing a global variable

The alternative PHP code:

    case 'variable:main':
        if($this->_getVar('item') == Opt_Class::ACCESS_LOCAL)
        {
            return 'myVariableReader(\''.$this->_getVar('item').'\')';
        }
        else
        {
            return 'myGlobalVariableReader(\''.$this->_getVar('item').'\')';
        }

Modifying the variable values

It is also possible to control the variable assignments via the variable:assign snippet. The new value is provided in the value format variable that must be placed somewhere in the returned code.

The value format variable actually contains neither PHP nor OPT expression that generates the specified value and there is no way to identify, what exactly the programmer is going to assign. The exact value is an internal token used by the expression engine to identify subexpressions.

A sample code:

    case 'variable:assign':
        return 'myVariableModifier(\''.$this->_getVar('item').'\', '.$this->_getVar('value').')';
5.7.1. Variables
5.7. New data formats
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5.7. New data formats
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5.7.2. Container items