080-DynamicTypes.md

Dynamic types

Blocks may use one of the following static types for inputs and outputs:

• string
• boolean
• float

Blocks may also support different types for inputs and outputs. The exact type for outputs should be provided by the block, possibly as a result of parameters or what inputs it has connected to it. Blocks can support different input types and inspect these; in which case, an any or Value type can be used as the $process parameter's type. What types of inputs are connected to a block are available from BlockBase.getInputTypeName when the $validate method is called. The $validate should throw an exception if the input types connected are incorrect.

Providing input types

Blocks typically declare what type an input is by specifying the parameter type of the $input_<name> parameter of the $process action, including the any type. However, as boolean is used for both boolean and pulse types, a block may also have a constant string $INPUT_TYPE_<inputId> constant which can be the value "pulse".

Providing output types

Blocks can declare what type an output is in the following ways:

• parameter type of the $setOutput action
• a constant string $OUTPUT_TYPE_<outputId>
• an action $outputType_<outputId>() returns string

At most, one of the string constant or action may be present on a block.

The string constant form, or the return value of the $outputType action, can be one of:

• boolean, string, float.
• pulse (to distinguish between boolean and pulse outputs).
• input(<inputId>) - the same type as the named input.
• sameAsAll(<inputId1>, <inputId2>, ...) - the same type as the named input. If any of the named input types are different, then this is treated as a validation error.
• pulseOrBoolean(<inputId1>, <inputId2>, ...) - if all of the named inputs are boolean, then the output type is boolean. If any of the inputs are a pulse type, then the output is a pulse type.

The $setOutput parameter type should be compatible with what types the block will generate. For pulseOrBoolean, a boolean is sufficient; in other cases, a Value or any type should be used.

For example, the following block performs an "add" operation on float or string types, but not on a mixture:

event Add {
    BlockBase $base;
    action $process(Activation $activation, any $input_value1, any $input_value2) {
        switch($input_value1) {
            case float: {
                $setOutput_added($activation, $input_value1 + (<float>$input_value2));
            }
            case string: {
                $setOutput_added($activation, $input_value1 + (<string>$input_value2));
            }
        }
    }
    action<Activation, any> $setOutput_added;
    constant string $OUTPUT_TYPE_added := "sameAsAll(value1, value2)";
}

Using the constant sameAsAll is equivalent to:

event Add {
    BlockBase $base;
    action $validate() {
        if $base.getInputTypeName("value1") != $base.getInputTypeName("value2") {
            throw L10N.getLocalizedException_basic("block_msg_Add_DifferentTypes");
        }
    }
    action $process(Activation $activation, any $input_value1, any $input_value2) {
        switch($input_value1) {
            case float: {
                $setOutput_added($activation, $input_value1 + (<float>$input_value2));
            }
            case string: {
                $setOutput_added($activation, $input_value1 + (<string>$input_value2));
            }
        }
    }
    action<Activation, any> $setOutput_added;
    action $outputType_added() returns string {
        return $base.getInputTypeName("value1");
    }
}

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