Sunday, October 23, 2011

#1 essential classificationS of variables in each language - java, c++ and c#

In java, a variable is exactly one of 2 -- reference var or primitive var. Therefore, a thingy/entity (more precisely an"allocation") is either an OBJECT or a primitive. Clean and simple.

C++ doesn't differentiate between primitives and composite objects. However, it does differentiate between allocation locations. In C++, an entity either lives on heap, on stack or global area, with important differences. The word "object" has no special meaning.

See also http://bigblog.tanbin.com/2009/06/primitive-vs-object-dichotomy-not-in-c.html
See also http://bigblog.tanbin.com/2011/04/pbref-pbclone-in-any-language.html

In C#, avoid the word "object" if possible. The real, deep and precise (less clean than java) dichotomy is value-type vs reference type.
* a reference type variable occupies 32 bits on a 32-bit machine. The pointee is always on heap, and could be 99 Bytes.
* a value type variable is like a nonref in c++ and occupies 99B. Unlike reference type variables, there's no separate storage for the variable.
* See http://bigblog.tanbin.com/2011/10/rooted-vs-reseat-able-variables-c-c.html

- assignment to a reference type var copies the RHS 32 bit address and reseats the LHS pointer. Same as java.
- assignment to a value type var bulldozes the LHS and clones the 99B into it.
**Java only clones primitives, up to 64 bits.
**C++ can clone any variable if you pass-by-value.

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http://www.linkedin.com/in/tanbin