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Algebrical Data Types in C++

Update: next post is here

The subtitle of this post could be C++11 is cool, but let's start from the beginning.

The starting point is the long standing argument on reporting error states of functions by means of exceptions or by multivalued functions. Recent languages such as Go by Google and Swift by Apple prefer to manage error states in the second form, while C++ and Java are biased toward exceptions (See [6] for a discussion). 

Multivalued functions are based on the concept of sum-types, also called algebrical types in other languages such as Haskell, or tagged unions. A sum-type is defined by a list of types, and a sum-type variable contains a typed value from such a list. A sum-type is similar to unions, except that the current type of the union is managed automatically; also a sum-type can be considered complementary to C++11 tuples. In particular we can say:
multi-type, single-value: sum-type/variant multi-type, multi-value:  tuplesingle-type, multi-value: vector or array …