From b0992869c0cf9caf865f5e41016d0fb652dd7a1c Mon Sep 17 00:00:00 2001
From: James Ahlborn <jtahlborn@yahoo.com>
Date: Thu, 15 Dec 2016 03:53:22 +0000
Subject: [PATCH] add method for indicating purity of an expression, possible
 use for future caching

git-svn-id: https://svn.code.sf.net/p/jackcess/code/jackcess/branches/exprs@1069 f203690c-595d-4dc9-a70b-905162fa7fd2
---
 .../jackcess/expr/Function.java               |  1 +
 .../jackcess/impl/expr/DefaultFunctions.java  |  4 +
 .../jackcess/impl/expr/Expressionator.java    | 73 +++++++++++++++++++
 3 files changed, 78 insertions(+)

diff --git a/src/main/java/com/healthmarketscience/jackcess/expr/Function.java b/src/main/java/com/healthmarketscience/jackcess/expr/Function.java
index 9b250b3..10ecc2b 100644
--- a/src/main/java/com/healthmarketscience/jackcess/expr/Function.java
+++ b/src/main/java/com/healthmarketscience/jackcess/expr/Function.java
@@ -24,4 +24,5 @@ public interface Function
 {
   public String getName();
   public Value eval(Value... params);
+  public boolean isPure();
 }
diff --git a/src/main/java/com/healthmarketscience/jackcess/impl/expr/DefaultFunctions.java b/src/main/java/com/healthmarketscience/jackcess/impl/expr/DefaultFunctions.java
index 70ff3cc..613c276 100644
--- a/src/main/java/com/healthmarketscience/jackcess/impl/expr/DefaultFunctions.java
+++ b/src/main/java/com/healthmarketscience/jackcess/impl/expr/DefaultFunctions.java
@@ -55,6 +55,10 @@ public class DefaultFunctions
       return _name;
     }
 
+    public boolean isPure() {
+      return true;
+    }
+
     protected void validateNumParams(Value[] params) {
       int num = params.length;
       if((num < _minParams) || (num > _maxParams)) {
diff --git a/src/main/java/com/healthmarketscience/jackcess/impl/expr/Expressionator.java b/src/main/java/com/healthmarketscience/jackcess/impl/expr/Expressionator.java
index 5d9c1d1..f8f6e12 100644
--- a/src/main/java/com/healthmarketscience/jackcess/impl/expr/Expressionator.java
+++ b/src/main/java/com/healthmarketscience/jackcess/impl/expr/Expressionator.java
@@ -360,6 +360,9 @@ public class Expressionator
   
 
   private static final Expr THIS_COL_VALUE = new Expr() {
+    @Override public boolean isPure() {
+      return false;
+    }
     @Override protected Value eval(RowContext ctx) {
       return ctx.getThisColumnValue();
     }
@@ -1170,6 +1173,24 @@ public class Expressionator
     return paramVals;
   }
 
+  private static boolean arePure(List<Expr> exprs) {
+    for(Expr expr : exprs) {
+      if(!expr.isPure()) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  private static boolean arePure(Expr... exprs) {
+    for(Expr expr : exprs) {
+      if(!expr.isPure()) {
+        return false;
+      }
+    }
+    return true;
+  }
+
   private static void literalStrToString(String str, StringBuilder sb) {
     sb.append("\"")
       .append(str.replace("\"", "\"\""))
@@ -1394,6 +1415,8 @@ public class Expressionator
       return outerExpr;
     }
     
+    public abstract boolean isPure();
+
     protected abstract Value eval(RowContext ctx);
 
     protected abstract void toExprString(StringBuilder sb, boolean isDebug);
@@ -1409,6 +1432,11 @@ public class Expressionator
       _str = str;
     }
 
+    @Override
+    public boolean isPure() {
+      return true;
+    }
+
     @Override 
     protected Value eval(RowContext ctx) {
       return _val;
@@ -1429,6 +1457,11 @@ public class Expressionator
       _val = toLiteralValue(valType, value, sdf);
     }
 
+    @Override
+    public boolean isPure() {
+      return true;
+    }
+
     @Override
     public Value eval(RowContext ctx) {
       return _val;
@@ -1459,6 +1492,11 @@ public class Expressionator
       _fieldName = fieldName;
     }
 
+    @Override
+    public boolean isPure() {
+      return false;
+    }
+
     @Override
     public Value eval(RowContext ctx) {
       return ctx.getRowValue(_collectionName, _objName, _fieldName);
@@ -1484,6 +1522,11 @@ public class Expressionator
       _expr = expr;
     }
 
+    @Override
+    public boolean isPure() {
+      return _expr.isPure();
+    }
+
     @Override
     protected Value eval(RowContext ctx) {
       return _expr.eval(ctx);
@@ -1507,6 +1550,11 @@ public class Expressionator
       _params = params;
     }
 
+    @Override
+    public boolean isPure() {
+      return _func.isPure() && arePure(_params);
+    }
+
     @Override
     protected Value eval(RowContext ctx) {
       return _func.eval(exprListToValues(_params, ctx));
@@ -1537,6 +1585,11 @@ public class Expressionator
       _right = right;
     }
 
+    @Override
+    public boolean isPure() {
+      return arePure(_left, _right);
+    }
+    
     public OpType getOp() {
       return _op;
     }
@@ -1588,6 +1641,11 @@ public class Expressionator
       _expr = expr;
     }
 
+    @Override
+    public boolean isPure() {
+      return _expr.isPure();
+    }
+
     public OpType getOp() {
       return _op;
     }
@@ -1654,6 +1712,11 @@ public class Expressionator
       _expr = expr;
     }
 
+    @Override
+    public boolean isPure() {
+      return _expr.isPure();
+    }
+
     public OpType getOp() {
       return _op;
     }
@@ -1722,6 +1785,11 @@ public class Expressionator
       _exprs = exprs;
     }
 
+    @Override
+    public boolean isPure() {
+      return super.isPure() && arePure(_exprs);
+    }
+
     @Override
     protected Value eval(RowContext ctx) {
       return _op.eval(_expr.eval(ctx), 
@@ -1750,6 +1818,11 @@ public class Expressionator
       _endRangeExpr = endRangeExpr;
     }
 
+    @Override
+    public boolean isPure() {
+      return _expr.isPure() && arePure(_startRangeExpr, _endRangeExpr);
+    }
+
     public Expr getRight() {
       return _endRangeExpr;
     }
-- 
2.39.5