content: /* 
   * Kodkod -- Copyright (c) 2005-present, Emina Torlak
   *
   * Permission is hereby granted, free of charge, to any person obtaining a copy
   * of this software and associated documentation files (the "Software"), to deal
   * in the Software without restriction, including without limitation the rights
   * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
   * copies of the Software, and to permit persons to whom the Software is
   * furnished to do so, subject to the following conditions:
   *
   * The above copyright notice and this permission notice shall be included in
   * all copies or substantial portions of the Software.
   *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
   * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
   * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
   * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
   * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
   * THE SOFTWARE.
   */
  package kodkod.ast;
  
  import java.util.Arrays;
  import java.util.Iterator;
  
  import kodkod.ast.visitor.ReturnVisitor;
  import kodkod.ast.visitor.VoidVisitor;
  import kodkod.util.collections.Containers;
  
  /**
   * A general projection expression.  For example,
   * let [[e]] = {&lt;a, b, c&gt;, &lt;d, e, f&gt;, &lt;d, g, f&gt;}.  Then, 
   * project(e, 1, 3) = {&lt;a, c&gt;, &lt;d, f&gt;} and project(e, 1, 1, 2) = {&lt;a, a, b&gt;, &lt;d, d, e&gt;, &lt;d, d, g&gt;}.
   * 
   * @specfield expression: Expression 
   * @specfield columns: [0..arity) -> one IntExpression
   * @invariant children = 0->expression + { i: int, e: IntExpression | columns[i-1] = e }
   * @author Emina Torlak
   */
  public final class ProjectExpression extends Expression {
  	private final Expression expr;
  	private final IntExpression[] columns;
  
  	/**
  	 * Constructs a new projection expression using the given
  	 * expr and columns.
  	 * @ensures this.expression' = expr && this.indices' = columns
  	 */
  	ProjectExpression(Expression expr, IntExpression... columns) {
  		if (columns.length==0)
  			throw new IllegalArgumentException("No columns specified for projection.");
  		this.expr = expr;
  		this.columns = new IntExpression[columns.length];
  		System.arraycopy(columns, 0, this.columns, 0, columns.length);
  	}
  
  	/**
  	 * {@inheritDoc}
  	 * @see kodkod.ast.Expression#arity()
  	 */
  	public int arity() { return columns.length; }
  
  	/**
  	 * Returns this.expression.
  	 * @return this.expression 
  	 */
  	public Expression expression() { return expr; }
  	
  	/**
  	 * Returns an iterator over this.columns, in proper sequence.
  	 * @return an iterator over this.columns, in proper sequence
  	 */
  	public Iterator<IntExpression> columns() {
  		return Containers.iterate(columns);
  	}
  	
  	/**
  	 * Returns the ith column.
  	 * @requires 0 <= i < this.arity
  	 * @return this.columns[i]
  	 */
  	public IntExpression column(int i) { return columns[i]; }
  	
  	/**
  	 * {@inheritDoc}
  	 * @see kodkod.ast.Expression#accept(kodkod.ast.visitor.ReturnVisitor)
  	 */
  	@Override
  	public <E, F, D, I> E accept(ReturnVisitor<E, F, D, I> visitor) {
  		return visitor.visit(this);
  	}
  
  	/**
  	 * {@inheritDoc}
  	 * @see kodkod.ast.Node#accept(kodkod.ast.visitor.VoidVisitor)
  	 */
  	public void accept(VoidVisitor visitor) {
  		visitor.visit(this);	
  	}
  
  	/**
  	 * {@inheritDoc}
  	 * @see kodkod.ast.Node#toString()
  	 */
  	public String toString() {
  		return expr.toString() + Arrays.toString(columns);
  	}
  		
  }
  