我正在用 Java 編寫一個 AST 解釋器，它有很多方法可以檢查參數類型并在它們匹配時執行操作。到目前為止，已經有五種以上的方法，它們基本上是相互復制粘貼的版本。有沒有辦法抽象要檢查的類型和要執行的操作？ @Override public Object visitMultiplyNode(MultiplyNode multiplyNode) { Object lhs = multiplyNode.getLeftHandSide().accept(this); Object rhs = multiplyNode.getRightHandSide().accept(this); if (lhs instanceof Double && rhs instanceof Double) { return (double) lhs * (double) rhs; } if (lhs instanceof Long && rhs instanceof Long) { return (long) lhs * (long) rhs; } throw new TypeError("Can not multiply " + lhs.getClass() + " and " + rhs.getClass() + "."); }我要檢查的類型并不總是相同的，例如，模數節點只接受 Longs 而加法節點也接受 Strings 進行連接。 @Override public Object visitAddNode(AddNode addNode) { Object lhs = addNode.getLeftHandSide().accept(this); Object rhs = addNode.getRightHandSide().accept(this); if (lhs instanceof Double && rhs instanceof Double) { return (double) lhs + (double) rhs; } if (lhs instanceof Long && rhs instanceof Long) { return (long) lhs + (long) rhs; } if (lhs instanceof String && rhs instanceof String) { return "" + lhs + lhs; } throw new TypeError("Can not add " + lhs.getClass() + " and " + rhs.getClass() + "."); } @Override public Object visitModulusNode(ModulusNode modulusNode) { Object lhs = modulusNode.getLeftHandSide().accept(this); Object rhs = modulusNode.getRightHandSide().accept(this); if (lhs instanceof Long && rhs instanceof Long) { return (long) lhs % (long) rhs; } throw new TypeError("Can not take modulus of " + lhs.getClass() + " and " + rhs.getClass() + "."); }
2 回答
慕運維8079593
TA貢獻1876條經驗 獲得超5個贊
你可以使用 lambda：
private Object visitBinaryOperatorNode(BinaryOpNode node, BiFunction<T, T> op) {
Object lhs = node.getLeftHandSide().accept(this);
Object rhs = node.getRightHandSide().accept(this);
if (lhs instanceof Long && rhs instanceof Long) {
return op.apply((long) lhs, (long) rhs);
}
throw new TypeError("Can not take " + node.getOpName() + "of " + lhs.getClass() + " and " + rhs.getClass() + ".");
}
但是，由于您的某些運算符支持多種類型，因此您需要另一層抽象：
@RequiredArgsConstructor// Lombok, otherwise write the boilerplate yourself
public class BinaryOperator<T, T> {
@NonNull private final BiFunction<T, T> op;
@NonNull private final Class<T> clazz;
public boolean isApplicable(Object left, Object right) {
return clazz.isInstance(left) && clazz.isInstance(right);
}
public T apply(Object left, Object right) {
return op.apply(clazz.cast(left), clazz.cast(right));
}
}
您現在可以傳遞一組有效的二元運算符并測試它們是否適用，如果適用，則應用它們。
private static final List<BinaryOperator<?, ?>> VALID_ADD_OPERATORS = Arrays.asList(
new BinaryOperator<>((x, y) -> x + y, Double.class),
new BinaryOperator<>((x, y) -> x + y, Long.class),
new BinaryOperator<>((x, y) -> x + y, String.class)
);
private static final List<BinaryOperator<?, ?>> VALID_MULTIPLY_OPERATORS = Arrays.asList(
new BinaryOperator<>((x, y) -> x * y, Double.class),
new BinaryOperator<>((x, y) -> x * y, Long.class)
);
@Override
public Object visitAddNode(AddNode addNode) {
return visitBinaryOperatorNode(addNode, VALID_ADD_OPERATORS );
}
@Override
public Object visitMultiplyNode(MultiplyNode multiplyNode) {
return visitBinaryOperatorNode(multiplyNode, VALID_MULTIPLY_OPERATORS );
}
private Object visitBinaryOperatorNode(BinaryOpNode node, List<BinaryOperator<?, ?>> validOperators) {
Object lhs = node.getLeftHandSide().accept(this);
Object rhs = node.getRightHandSide().accept(this);
for (BinaryOperator<?, ?> op : validOperators) {
if (op.isApplicable(lhs, rhs)) return op.apply(lhs, rhs);
}
throw new TypeError("Can not take " + node.getOpName() + "of " + lhs.getClass() + " and " + rhs.getClass() + ".");
}
慕的地8271018
TA貢獻1796條經驗 獲得超4個贊
您可以將這些檢查提取到單獨的對象中，并在需要時重用它。
例如，通過為要處理轉換的每種類型定義一個枚舉值。
例如
public enum ConvertType {
DOUBLE {
Object apply(Object lhs, Object rhs) {
if (lhs instanceof Double && rhs instanceof Double) {
return (double) lhs + (double) rhs;
}
return null;
}
},
LONG {
Object apply(Object lhs, Object rhs) {
if (lhs instanceof Long && rhs instanceof Long) {
return (long) lhs + (long) rhs;
}
return null;
}
},
STRING {
Object apply(Object lhs, Object rhs) {
if (lhs instanceof String && rhs instanceof String) {
return "" + lhs + lhs;
}
return null;
}
};
public static Object apply(Object a, Object b, ConvertType... convertTypes) {
for (ConvertType convertType : convertTypes) {
Object result = convertType.apply(a, b);
if (result != null) {
return result;
}
}
throw new TypeError("Can not take modulus of " + a.getClass() + " and " + b.getClass() + ".");
}
}
轉換的入口點是靜態方法：
public static Object apply(Object a, Object b, ConvertType... convertTypes)
ConvertType多虧了var-args.
例如 ：
@Override
public Object visitMultiplyNode(MultiplyNode multiplyNode) {
Object lhs = multiplyNode.getLeftHandSide().accept(this);
Object rhs = multiplyNode.getRightHandSide().accept(this);
return ConvertType.apply(lhs , rhs, ConvertType.DOUBLE, ConvertType.LONG);
}
或者 ：
@Override
public Object visitAddNode(AddNode addNode) {
Object lhs = addNode.getLeftHandSide().accept(this);
Object rhs = addNode.getRightHandSide().accept(this);
return ConvertType.apply(lhs , rhs, ConvertType.DOUBLE, ConvertType.LONG, ConvertType.STRING);
}
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