International Organization for Standardization (ISO)
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ISO/IEC TR 25438:2006
Scope
The CLI standard libraries (ISO/IEC 23271) provide a collection of common types that can be used by multiple
languages. With the addition of generics to the CLI, the standard libraries have been extended to include a
number of common generic types, in particular, collections. However, at present, these libraries do not include
many simple generic types found in a number of different languages. Any language which uses these
common types must implement them rather than deferring to the CLI library, thereby reducing language interoperability.
This Technical Report addresses this issue by providing a number of these common types.
Generic tuples (product types) are standard in a number of languages: C++ (template Pair), Ada, Haskell,
and Standard ML (SML). However, languages differ in the number of pre-defined tuple sizes supported by
their standard libraries; e.g. C++ provides just one (Pair) while Haskell provides eight (sizes 2 to 9) and SML
allows any size of tuple. This Technical Report provides nine (sizes 2 to 10).
Generic programming encourages “higher order” programming where generic functions (methods) take
function (delegate) type arguments that have generic types. Examples include Ada’s with and generic
constraints, and function arguments in Haskell and SML. In the CLI, function values are provided in the form
of delegates, so this proposal defines standard generic delegate types for functions (which return a value) and
procedures (which do not).
Another two types that occur in a number of languages are an optional type, which either contains a value of
some other type or an indication that such a value is not present; and an either type, which holds a value of
one of two possible types and an indication of which one is present. This proposal provides both of these.
Note The optional type is similar to, but different from, the type System.Nullable.
Finally, in existing generic languages, a need has been found for a filler type to be used when a particular
generic parameter is not required for a particular use of the generic type. A standard one-value type is often
provided for this purpose, often called Unit or Void. This Technical Report includes such a type.
ISO/IEC TR 25438:2006 history
2006ISO/IEC TR 25438:2006 Information technology - Common Language Infrastructure (CLI) - Technical Report: Common Generics