1 files changed, 55 insertions, 0 deletions
diff --git a/hamcrest-core/src/org/hamcrest/core/DescribedAs.java b/hamcrest-core/src/org/hamcrest/core/DescribedAs.java
new file mode 100644
index 0000000..7b8c151
--- /dev/null
+++ b/hamcrest-core/src/org/hamcrest/core/DescribedAs.java
@@ -0,0 +1,55 @@
+/*  Copyright (c) 2000-2006 hamcrest.org
+ */
+package org.hamcrest.core;
+
+import java.util.regex.Pattern;
+
+import org.hamcrest.Description;
+import org.hamcrest.Matcher;
+import org.hamcrest.Factory;
+import org.hamcrest.BaseMatcher;
+
+/**
+ * Provides a custom description to another matcher.
+ */
+public class DescribedAs<T> extends BaseMatcher<T> {
+    private final String descriptionTemplate;
+    private final Matcher<T> matcher;
+    private final Object[] values;
+    
+    private final static Pattern ARG_PATTERN = Pattern.compile("%([0-9]+)"); 
+    
+    public DescribedAs(String descriptionTemplate, Matcher<T> matcher, Object[] values) {
+        this.descriptionTemplate = descriptionTemplate;
+        this.matcher = matcher;
+        this.values = values.clone();
+    }
+    
+    public boolean matches(Object o) {
+        return matcher.matches(o);
+    }
+
+    public void describeTo(Description description) {
+        java.util.regex.Matcher arg = ARG_PATTERN.matcher(descriptionTemplate);
+        
+        int textStart = 0;
+        while (arg.find()) {
+            description.appendText(descriptionTemplate.substring(textStart, arg.start()));
+            int argIndex = Integer.parseInt(arg.group(1));
+            description.appendValue(values[argIndex]);
+            textStart = arg.end();
+        }
+        
+        if (textStart < descriptionTemplate.length()) {
+            description.appendText(descriptionTemplate.substring(textStart));
+        }
+    }
+
+    /**
+     * Wraps an existing matcher and overrides the description when it fails.
+     */
+    @Factory
+    public static <T> Matcher<T> describedAs(String description, Matcher<T> matcher, Object... values) {
+        return new DescribedAs<T>(description, matcher, values);
+    }
+}