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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
"use strict";
module.metadata = {
"stability": "experimental"
};
const method = require("method/core");
// Utility function that is just an enhancement over `method` to
// allow predicate based dispatch in addition to polymorphic
// dispatch. Unfortunately polymorphic dispatch does not quite
// cuts it in the world of XPCOM where no types / classes exist
// and all the XUL nodes share same type / prototype.
// Probably this is more generic and belongs some place else, but
// we can move it later once this will be relevant.
var dispatcher = hint => {
const base = method(hint);
// Make a map for storing predicate, implementation mappings.
let implementations = new Map();
// Dispatcher function goes through `predicate, implementation`
// pairs to find predicate that matches first argument and
// returns application of arguments on the associated
// `implementation`. If no matching predicate is found delegates
// to a `base` polymorphic function.
let dispatch = (value, ...rest) => {
for (let [predicate, implementation] of implementations) {
if (predicate(value))
return implementation(value, ...rest);
}
return base(value, ...rest);
};
// Expose base API.
dispatch.define = base.define;
dispatch.implement = base.implement;
dispatch.toString = base.toString;
// Add a `when` function to allow extending function via
// predicates.
dispatch.when = (predicate, implementation) => {
if (implementations.has(predicate))
throw TypeError("Already implemented for the given predicate");
implementations.set(predicate, implementation);
};
return dispatch;
};
exports.dispatcher = dispatcher;
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