Attribute Type Coercion
From OpenLaszlo
Contents |
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Introduction
A way to convert attribute values to/from representations (as String).
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Proposal
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Overview
Introduce `Presentation Type`s that specify how to convert a corresponding language type to/from a string.
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Changes
//---
// PresentationType
//
// A presentation type is a specification of how to map a Javascript type to a String
// representation
//---
class PresentationType {
function accept(value) { return value; }
function present(value) { return "" + value; }
}
2 new methods on node, acceptAttribute and presentAttribute
//---
// acceptAttribute
// @param name:String the name of the attribute
// @param type:PresentationType
// @param value:String the string representation of the desired value
//
// Sets the named attribute to the result of converting the value using the
// type's accept method
//---
function acceptAttribute(name, type, value) {
this.setAttribute(name, type.accept(value));
}
//---
// presentAttribute
// @param name:String the name of the attribute
// @param type:PresentationType
// @returns value:String
//
// Returns the value of the named attribute converted to a string byt
// type's present method
//---
function presentAttribute(name, type) {
return type.present(this.getAttribute(name));
}
Define a mapping table from the space of types for attributes to PresentationTypes.
Finally, for $path and $style constraints, the compiler will emit a constraint function that uses `acceptAttribute` to bind attributes, rather than setAttribute, according to the mapping table.
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Examples
//---
// Example presentation type
//---
class BooleanPresentationType extends PresentationType {
function accept(value) {
switch (value.toLowerCase()) {
case "0": case "false":
return false;
default:
return true;
}
}
function present(value) {
if (value) {
return "true";
} else {
return "false";
}
}
(And so on, for other types.)
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