String interning

05 February 2014

	[Test]
    public void StringReferenceNotSameTest()
    {
        var he = "he";
        var hello = "hello";
        var hello2 = he + "llo";
        Assert.False(ReferenceEquals(hello,hello2));
        Assert.AreNotSame(hello,hello2);
    }

    [Test]
    public void StringSameReferenceTest()
    {
        var hello = "hello";
        var hello2 = "he" + "llo";
        Assert.True(ReferenceEquals(hello, hello2));
        Assert.AreSame(hello, hello2);
    }

consider these two tests, the first test will create three object in the heap, because he is not const, so clr didn’t treat it as same as “hello”, there will be three object, “he”, and two same “hello”

the second test, will create only one object as he here is const

so when concat string, don’t write such code

var str = "abc";
var str2 = str + "bcd";

instead

var str2 = "abc" + "bcd";

so when there is also “abcbcd” in the heap, clr will not create a new object

csharp 4

csharp 1