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// Copyright 2017 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.searchlib.rankingexpression.evaluation;
import com.yahoo.searchlib.rankingexpression.rule.Arguments;
import com.yahoo.tensor.evaluation.EvaluationContext;
import java.util.Set;
/**
* <p>The context providing value bindings for an expression evaluation.</p>
*
* @author bratseth
*/
public abstract class Context implements EvaluationContext {
/**
* <p>Returns the value of a simple variable name.</p>
*
* @param name The name of the variable whose value to return.
* @return The value of the named variable.
*/
public abstract Value get(String name);
/**
* <p>Returns the value of a <i>structured variable</i> on the form
* <code>name(argument*)(.output)?</code>, where <i>argument</i> is any
* string. This may be used to implement more advanced variables whose
* values are calculated at runtime from arguments. Supporting this in a
* context is optional. Implementations may choose to throw
* UnsupportedOperationException or always return null, or to handle outputs
* but not arguments.</p>
*
* <p>This default implementation does the latter - if arguments is non-null
* and non-empty an UnsupportedOperationException is thrown, otherwise
* get(name + "." + output) is called (or just get(name)) if output is also
* null.</p>
*
* @param name The name of this variable.
* @param arguments The parsed arguments as given in the textual expression.
* @param output The name of the value to output (to enable one named
* calculation to output several), or null to output the
* "main" (or only) value.
*/
public Value get(String name, Arguments arguments,String output) {
if (arguments!=null && arguments.expressions().size() > 0)
throw new UnsupportedOperationException(this + " does not support structured ranking expression variables, attempted to reference '" +
name + arguments + "'");
if (output==null)
return get(name);
return get(name + "." + output);
}
/**
* <p>Lookup by index rather than name. This is supported by some optimized
* context subclasses. This default implementation throws
* UnsupportedOperationException.</p>
*
* @param index The index of the variable whose value to return.
* @return The value of the indexed variable.
*/
public Value get(int index) {
throw new UnsupportedOperationException(this + " does not support variable lookup by index");
}
/**
* <p>Lookup by index rather than name directly to a double. This is supported by some optimized
* context subclasses. This default implementation throws
* UnsupportedOperationException.</p>
*
* @param index The index of the variable whose value to return.
* @return The value of the indexed variable.
*/
public double getDouble(int index) {
throw new UnsupportedOperationException(this + " does not support variable lookup by index");
}
/**
* Same as put(name,DoubleValue.frozen(value))
*/
public final void put(String name, double value) {
put(name, DoubleValue.frozen(value));
}
/**
* <p>Sets a value to this, or throws an UnsupportedOperationException if
* this is not supported. This default implementation does the latter.</p> *
*
* @param name The name of the variable to set.
* @param value the value to set. Ownership of this value is transferred to this - if it is mutable
* (not frozen) it may be modified during execution
* @since 5.1.5
*/
public void put(String name, Value value) {
throw new UnsupportedOperationException(this + " does not support variable assignment");
}
/**
* <p>Returns all the names available in this, or throws an
* UnsupportedOperationException if this operation is not supported. This
* default implementation does the latter.</p>
*
* @return The set of all variable names.
*/
public Set<String> names() {
throw new UnsupportedOperationException(this + " does not support return a list of its names");
}
}
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