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函数重载库Overload

2009-07-02 14:24 by Cat Chen, 127 visits, 网摘, 收藏, 编辑
(function() {
    Overload = {};

    var copySignature = function(signature) {
        var copy = [];
        for (var i = 0; i < signature.length; i++) {
            copy.push(signature[i]);
        }
        if (signature.arguments) {
            copy.arguments = true;
        }
        return copy;
    };
    
    var inheritanceComparator = function(type1, type2) {
        if (type1 == type2) {
            return 0;
        } else if (type2 == Overload.Any) {
            return 1;
        } else if (type1 == Overload.Any) {
            return -1;
        } else if (type1.prototype instanceof type2) {
            return 1;
        } else if (type2.prototype instanceof type1) {
            return -1;
        } else {
            return 0;
        }
    };
    
    var overloadComparator = function(overload1, overload2) {
        var signature1Better = false;
        var signature2Better = false;
        var signature1 = overload1.signature;
        var signature2 = overload2.signature;
        if (!signature1.more && signature2.more) {
            signature1Better = true;
            signature1 = copySignature(signature1);
            signature1.length = signature2.length;
        } else if (signature1.more && !signature2.more) {
            signature2Better = true;
            signature2 = copySignature(signature2);
            signature2.length = signature1.length;
        } else if(signature1.more && signature2.more) {
            if (signature1.length > signature2.length) {
                signature2 = copySignature(signature2);
                while (signature2.length < signature1.length) {
                    signature2[signature2.length] = Overload.Any;
                }
            } else if (signature1.length < signature2.length) {
                signature1 = copySignature(signature1);
                while (signature1.length < signature2.length) {
                    signature1[signature1.length] = Overload.Any;
                }
            }
        }
        for (var i = 0; i < signature1.length; i++) {
            var comparison = inheritanceComparator(signature1[i], signature2[i]);
            if (comparison > 0) {
                signature1Better = true;
            } else if (comparison < 0) {
                signature2Better = true;
            }
        }
        if (signature1Better && !signature2Better) {
            return 1;
        } else if (!signature1Better && signature2Better) {
            return -1;
        } else {
            return 0;
        }
    };
    
    var matchSignature = function(argumentsArray, signature) {
        if (argumentsArray.length < signature.length) {
            return false;
        } else if (argumentsArray.length > signature.length && !signature.more) {
            return false;
        }
        for (var i = 0; i < signature.length; i++) {
            if (!(signature[i] == Overload.Any
                || argumentsArray[i] instanceof signature[i]
                || argumentsArray[i].constructor == signature[i])) {
                    return false;
            }
        }
        return true;
    };
    
    Overload.create = function(overloadsArray) {
        var overloads = [];
        
        var select = function(argumentsArray) {
            var matches = [];
            for (var i = 0; i < overloads.length; i++) {
                if (matchSignature(argumentsArray, overloads[i].signature)) {
                    matches.push(overloads[i]);
                }
            }
            switch (matches.length) {
                case 0:
                    return null;
                case 1:
                    return matches[0]["function"];
                default:
                    matches = matches.sort(overloadComparator);
                    if (overloadComparator(matches[matches.length - 1], matches[matches.length - 2]) > 0) {
                        return matches[matches.length - 1]["function"];
                    } else {
                        return null;
                    }
            }
        };
        
        var overloaded = function() {
            var overload = select(arguments);
            if (overload) {
                return overload.apply(this, arguments);
            } else {
                throw "cannot select a proper overload";
            }
        };
        
        overloaded.select = select;
        
        overloaded.add = function(signature, overload) {
            if (signature instanceof Array) {
                signature = copySignature(signature);
            } else if (signature.constructor == String) {
                if (signature.replace(/(^\s+|\s+$)/ig, "") == "") {
                    signature = [];
                } else {
                    signature = signature.split(",");
                    for (var i = 0; i < signature.length; i++) {
                        var typeExpression = signature[i].replace(/(^\s+|\s+$)/ig, "");
                        var type = null;
                        if (typeExpression == "*") {
                            type = Overload.Any;
                        } else if (typeExpression == "...") {
                            type = Overload.More;
                        } else {
                            try {
                                type = eval("(" + typeExpression + ")");
                            } catch (error) {
                                throw "type expression cannot be evaluated: " + typeExpression;
                            }
                        }
                        signature[i] = type;
                    }
                }
            } else {
                throw "signature is neither a string nor an array";
            }
            for (var i = 0; i < signature.length; i++) {
                if (!(signature[i] instanceof Function)) {
                    throw "argument type should be a function";
                }
                if (i < signature.length - 1 && signature[i] == Overload.More) {
                    throw "arguments type cannot be used in any argument except the last one";
                }
            }
            if (signature[signature.length - 1] == Overload.More) {
                signature.length = signature.length - 1;
                signature.more = true;
            }
            overloads.push({
                "signature": signature,
                "function": overload
            });
            return this;
        };
        
        return overloaded;
    };
    
    Overload.add = function(signature, overload) {
        return Overload.create().add(signature, overload);
    };
    
    Overload.Any = function any() {
        throw "this type is only an identifier and should not be instantiated"
    };

    Overload.More = function more() {
        throw "this type is only an identifier and should not be instantiated"
    };
})();
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