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Google App Engine compliant variation of FreeMarker.
FreeMarker is a "template engine"; a generic tool to generate text output based on templates.
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
package freemarker.core;
import java.util.List;
import freemarker.template.TemplateException;
import freemarker.template.TemplateModel;
/**
* A local lambada expression is a lambda expression that creates a function that can only be called from the same
* context where it was created, and thus it doesn't need closure support. As of this writing (2019-02), this is the
* only kind of lambda expression supported, as supporting closures would add overhead to many basic operations, while
* local lambdas are "good enough" for the main use cases in templates (for filtering/transforming lists). Also,
* closures can be quite confusing when the lambda expression refers to variables that are not effectively final,
* such as a loop variable. So that's yet another issue to address if we go for less restricted lambdas.
*/
final class LocalLambdaExpression extends Expression {
private final LambdaParameterList lho;
private final Expression rho;
LocalLambdaExpression(LambdaParameterList lho, Expression rho) {
this.lho = lho;
this.rho = rho;
}
@Override
public String getCanonicalForm() {
return lho.getCanonicalForm() + " -> " + rho.getCanonicalForm();
}
@Override
String getNodeTypeSymbol() {
return "->";
}
@Override
TemplateModel _eval(Environment env) throws TemplateException {
throw new TemplateException("Can't get lambda expression as a value: Lambdas currently can only be used on a " +
"few special places.",
env);
}
/**
* Call the function defined by the lambda expression; overload specialized for 1 argument, the most common case.
*/
TemplateModel invokeLambdaDefinedFunction(TemplateModel argValue, Environment env) throws TemplateException {
return env.evaluateWithNewLocal(rho, lho.getParameters().get(0).getName(),
argValue != null ? argValue : TemplateNullModel.INSTANCE);
}
@Override
boolean isLiteral() {
// As we don't support true lambdas, they can't be evaluted in parse time.
return false;
}
@Override
protected Expression deepCloneWithIdentifierReplaced_inner(
String replacedIdentifier, Expression replacement, ReplacemenetState replacementState) {
for (Identifier parameter : lho.getParameters()) {
if (parameter.getName().equals(replacedIdentifier)) {
// As Expression.deepCloneWithIdentifierReplaced was exposed to users back then, now we can't add
// "throws ParseException" to this, therefore, we use UncheckedParseException as a workaround.
throw new UncheckedParseException(new ParseException(
"Escape placeholder (" + replacedIdentifier + ") can't be used in the " +
"parameter list of a lambda expressions.", this));
}
}
return new LocalLambdaExpression(
lho,
rho.deepCloneWithIdentifierReplaced(replacedIdentifier, replacement, replacementState));
}
@Override
int getParameterCount() {
return lho.getParameters().size() + 1;
}
@Override
Object getParameterValue(int idx) {
int paramCount = getParameterCount();
if (idx < paramCount - 1) {
return lho.getParameters().get(idx);
} else if (idx == paramCount - 1) {
return rho;
} else {
throw new IndexOutOfBoundsException();
}
}
@Override
ParameterRole getParameterRole(int idx) {
int paramCount = getParameterCount();
if (idx < paramCount - 1) {
return ParameterRole.ARGUMENT_NAME;
} else if (idx == paramCount - 1) {
return ParameterRole.VALUE;
} else {
throw new IndexOutOfBoundsException();
}
}
LambdaParameterList getLambdaParameterList() {
return lho;
}
/** The left side of the `->`. */
static class LambdaParameterList {
private final Token openingParenthesis;
private final Token closingParenthesis;
private final List parameters;
public LambdaParameterList(Token openingParenthesis, List parameters, Token closingParenthesis) {
this.openingParenthesis = openingParenthesis;
this.closingParenthesis = closingParenthesis;
this.parameters = parameters;
}
/** Maybe {@code null} */
public Token getOpeningParenthesis() {
return openingParenthesis;
}
/** Maybe {@code null} */
public Token getClosingParenthesis() {
return closingParenthesis;
}
public List getParameters() {
return parameters;
}
public String getCanonicalForm() {
if (parameters.size() == 1) {
return parameters.get(0).getCanonicalForm();
} else {
StringBuilder sb = new StringBuilder();
sb.append('(');
for (int i = 0; i < parameters.size(); i++) {
if (i != 0) {
sb.append(", ");
}
Identifier parameter = parameters.get(i);
sb.append(parameter.getCanonicalForm());
}
sb.append(')');
return sb.toString();
}
}
}
}