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// Copyright 2014 Google Inc. All rights reserved.
//
// Licensed 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 com.google.devtools.build.lib.syntax;
import com.google.common.base.Preconditions;
import com.google.devtools.build.lib.events.Location;
import java.io.Serializable;
/**
* Class representing an LValue.
* It appears in assignment, for loop and comprehensions, e.g.
* lvalue = 2
* [for lvalue in exp]
* for lvalue in exp: pass
* An LValue can be a simple variable or something more complex like a tuple.
*/
public class LValue implements Serializable {
// Currently, expr can only be an Ident, but we plan to support more.
private final Expression expr;
public LValue(Expression expr) {
this.expr = expr;
}
public Expression getExpression() {
return expr;
}
/**
* Assign a value to an LValue and update the environment.
*/
public void assign(Environment env, Location loc, Object result)
throws EvalException, InterruptedException {
if (!(expr instanceof Ident)) {
throw new EvalException(loc,
"can only assign to variables, not to '" + expr + "'");
}
Ident ident = (Ident) expr;
Preconditions.checkNotNull(result, "trying to assign null to %s", ident);
if (env.isSkylarkEnabled()) {
// The variable may have been referenced successfully if a global variable
// with the same name exists. In this case an Exception needs to be thrown.
SkylarkEnvironment skylarkEnv = (SkylarkEnvironment) env;
if (skylarkEnv.hasBeenReadGlobalVariable(ident.getName())) {
throw new EvalException(loc, "Variable '" + ident.getName()
+ "' is referenced before assignment."
+ "The variable is defined in the global scope.");
}
Class<?> variableType = skylarkEnv.getVariableType(ident.getName());
Class<?> resultType = EvalUtils.getSkylarkType(result.getClass());
if (variableType != null && !variableType.equals(resultType)
&& !resultType.equals(Environment.NoneType.class)
&& !variableType.equals(Environment.NoneType.class)) {
throw new EvalException(loc, String.format("Incompatible variable types, "
+ "trying to assign %s (type of %s) to variable %s which is already %s",
EvalUtils.prettyPrintValue(result),
EvalUtils.getDataTypeName(result),
ident.getName(),
EvalUtils.getDataTypeNameFromClass(variableType)));
}
}
env.update(ident.getName(), result);
}
void validate(ValidationEnvironment env, Location loc, SkylarkType rvalueType)
throws EvalException {
// TODO(bazel-team): Implement other validations.
if (expr instanceof Ident) {
Ident ident = (Ident) expr;
env.update(ident.getName(), rvalueType, loc);
return;
}
throw new EvalException(loc,
"can only assign to variables, not to '" + expr + "'");
}
@Override
public String toString() {
return expr.toString();
}
}
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