content: package com.alibaba.qlexpress4.runtime.instruction;
  
  import com.alibaba.qlexpress4.QLOptions;
  import com.alibaba.qlexpress4.exception.ErrorReporter;
  import com.alibaba.qlexpress4.runtime.QContext;
  import com.alibaba.qlexpress4.runtime.QResult;
  import com.alibaba.qlexpress4.runtime.trace.ExpressionTrace;
  import com.alibaba.qlexpress4.utils.PrintlnUtils;
  
  import java.util.function.Consumer;
  
  /**
   * Operation: no op, only for tracing peek value of stack
   * Input: 0
   * Output: 0
   *
   * Author: DQinYuan
   */
  public class TracePeekInstruction extends QLInstruction {
      
      private final Integer traceKey;
      
      public TracePeekInstruction(ErrorReporter errorReporter, Integer traceKey) {
          super(errorReporter);
          this.traceKey = traceKey;
      }
      
      @Override
      public QResult execute(QContext qContext, QLOptions qlOptions) {
          ExpressionTrace expressionTrace = qContext.getTraces().getExpressionTraceByKey(traceKey);
          if (expressionTrace != null) {
              expressionTrace.valueEvaluated(qContext.peek().get());
          }
          return QResult.NEXT_INSTRUCTION;
      }
      
      @Override
      public int stackInput() {
          return 0;
      }
      
      @Override
      public int stackOutput() {
          return 0;
      }
      
      @Override
      public void println(int index, int depth, Consumer<String> debug) {
          PrintlnUtils.printlnByCurDepth(depth, index + ": TracePeek " + traceKey, debug);
      }
  }
  