Every compile-time constant expression that is of type String will be put into the String pool. Essentially that means: if the compiler can (easily) “calculate” the value of the String without running the program, then it will be put into the pool (the rules are slightly more complicated than that and have a few corner … Read more
Identical literal strings are not guaranty to be identical, but you can build type from it which can compare identical (without comparing string), something like: // Sequence of char template <char…Cs> struct char_sequence { template <char C> using push_back = char_sequence<Cs…, C>; }; // Remove all chars from char_sequence from ‘\0’ template <typename, char…> struct … Read more
String literals get interned automatically (so, if your code contains “lalala” 1000 times, only one instance will exist). Such strings will not get GC’d and any time they are referenced the reference will be the interned one. string.Intern is there for strings that are not literals – say from user input or read from a … Read more
This is not undefined behavior, but unspecified behavior. For string literals, The compiler is allowed, but not required, to combine storage for equal or overlapping string literals. That means that identical string literals may or may not compare equal when compared by pointer. That means the result of A == B might be true or … Read more
Strings are immutable in Python, so the implementation can decide whether to intern (that’s a term often associated with C#, meaning that some strings are stored in a pool) strings or not. In your example, you’re dynamically creating strings. CPython does not always look into the pool to detect whether the string is already there … Read more
String literals are interned. As of Java 7, the HotSpot JVM puts interned Strings in the heap, not permgen. Prior to java 7, hotspot put interned Strings in permgen. However, interned Strings in permgen were garbage collected. Apparently, Class objects in permgen are also collectable, so everything in permgen is collectable, though permgen collection might … Read more
This is a technique to ensure that CONSTANT is not actually a constant. When the Java compiler sees a reference to a final static primitive or String, it inserts the actual value of that constant into the class that uses it. If you then change the constant value in the defining class but don’t recompile … Read more
It seems that JDK7 process intern in a different way as before. I tested it with build 1.7.0-b147 and got “both are equal”, but when executing it (same bytecode) with 1,6.0_24 I do not get the message. It also depends where the String b2 =… line is located in the source code. The following code … Read more
This is called interning, and yes, Python does do this to some extent, for shorter strings created as string literals. See About the changing id of an immutable string for some discussion. Interning is runtime dependent, there is no standard for it. Interning is always a trade-off between memory use and the cost of checking … Read more
In general, interning is something that just happens, automatically, when you use literal string values. Interning provides the benefit of only having one copy of the literal in memory, no matter how often it’s used. That being said, it’s rare that there is a reason to intern your own strings that are generated at runtime, … Read more