adds configuration possibility to allow/disallow to overwrite constan…

…t (allowed is default)

docs/configuration/configuration.md

@@ -13,6 +13,7 @@ Example usage, showing all default configuration values:
 
 ```java
 ExpressionConfiguration configuration = ExpressionConfiguration.builder()
+ .allowOverwriteConstants(true)
  .arraysAllowed(true)
  .dataAccessorSupplier(MapBasedDataAccessor::new)
  .decimalPlacesRounding(ExpressionConfiguration.DECIMAL_PLACES_ROUNDING_UNLIMITED)
@@ -22,12 +23,18 @@ ExpressionConfiguration configuration = ExpressionConfiguration.builder()
  .mathContext(ExpressionConfiguration.DEFAULT_MATH_CONTEXT)
  .operatorDictionary(ExpressionConfiguration.StandardOperatorsDictionary)
  .powerOfPrecedence(OperatorIfc.OPERATOR_PRECEDENCE_POWER)
+ .stripTrailingZeros(true)
  .structuresAllowed(true)
  .build();
 
 Expression expression = new Expression("2.128 + a", configuration);
 ```
 
+### Allow to Overwrite Constants
+
+If set to true (default), then variables can be set that have the name of a constant. In that case,
+the constant value will be removed and a variable value will be set.
+
 ### Arrays allowed
 
 Specifies if the array index function is allowed (default is true). If set to false, the expression

src/main/java/com/ezylang/evalex/Expression.java

@@ -253,6 +253,14 @@ public void validate() throws ParseException {
  * @return The Expression instance, to allow chaining of methods.
  */
  public Expression with(String variable, Object value) {
+ if (constants.containsKey(variable)) {
+ if (configuration.isAllowOverwriteConstants()) {
+ constants.remove(variable);
+ } else {
+ throw new UnsupportedOperationException(
+ String.format("Can't set value for constant '%s'", variable));
+ }
+ }
  getDataAccessor().setData(variable, new EvaluationValue(value));
  return this;
  }
@@ -281,7 +289,7 @@ public Expression and(String variable, Object value) {
  */
  public Expression withValues(Map<String, Object> values) {
  for (Map.Entry<String, Object> entry : values.entrySet()) {
- getDataAccessor().setData(entry.getKey(), new EvaluationValue(entry.getValue()));
+ with(entry.getKey(), entry.getValue());
  }
  return this;
  }

src/main/java/com/ezylang/evalex/config/ExpressionConfiguration.java

@@ -270,6 +270,12 @@ public class ExpressionConfiguration {
  */
  @Builder.Default @Getter private final boolean stripTrailingZeros = true;
 
+ /**
+ * If set to true (default), then variables can be set that have the name of a constant. In that
+ * case, the constant value will be removed and a variable value will be set.
+ */
+ @Builder.Default @Getter private final boolean allowOverwriteConstants = true;
+
  /**
  * Convenience method to create a default configuration.
  *

src/test/java/com/ezylang/evalex/ExpressionEvaluatorConstantsTest.java

@@ -16,6 +16,7 @@
 package com.ezylang.evalex;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
 
 import com.ezylang.evalex.config.ExpressionConfiguration;
 import com.ezylang.evalex.data.EvaluationValue;
@@ -62,4 +63,28 @@ void testCustomConstantsMixedCase() throws EvaluationException, ParseException {
 
  assertThat(expression.evaluate().getStringValue()).isEqualTo("6.4");
  }
+
+ @Test
+ void testOverwriteConstantsWith() throws EvaluationException, ParseException {
+ Expression expression = new Expression("e");
+ assertThat(expression.with("e", 9).evaluate().getStringValue()).isEqualTo("9");
+ }
+
+ @Test
+ void testOverwriteConstantsWithValues() throws EvaluationException, ParseException {
+ Map<String, Object> values = new HashMap<>();
+ values.put("E", 6);
+ Expression expression = new Expression("e");
+ assertThat(expression.withValues(values).evaluate().getStringValue()).isEqualTo("6");
+ }
+
+ @Test
+ void testOverwriteConstantsNotAllowed() {
+ Expression expression =
+ new Expression(
+ "e", ExpressionConfiguration.builder().allowOverwriteConstants(false).build());
+ assertThatThrownBy(() -> expression.with("e", 9).evaluate())
+ .isInstanceOf(UnsupportedOperationException.class)
+ .hasMessage("Can't set value for constant 'e'");
+ }
 }

src/test/java/com/ezylang/evalex/config/ExpressionConfigurationTest.java

@@ -53,6 +53,7 @@ void testDefaultSetup() {
  assertThat(configuration.getDecimalPlacesRounding())
  .isEqualTo(ExpressionConfiguration.DECIMAL_PLACES_ROUNDING_UNLIMITED);
  assertThat(configuration.isStripTrailingZeros()).isTrue();
+ assertThat(configuration.isAllowOverwriteConstants()).isTrue();
  }
 
  @Test