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{{Primary sources|date=September 2017}}
'''Uniform Function Call Syntax''' ('''UFCS''') or '''Uniform Calling Syntax''' ('''UCS''') or sometimes '''Universal Function Call Syntax''' is a [[programming language]] feature in [[D (programming language)|D]] and [[Nim (programming language)|Nim]] that allows any [[function (computer programming)|function]] to be called using the syntax for method calls (as in [[object-oriented programming]]), by using the [[receiver (object oriented programming)|receiver]] as the first parameter, and the given arguments as the remaining parameters.<ref>{{cite web|url=http://dlang.org/function.html#pseudo-member|title=Functions - D Programming Language|website=Dlang.org|accessdate=1 October 2017}}</ref> UFCS is particularly useful when function calls are chained<ref>{{cite web|url=http://ddili.org/ders/d.en/ufcs.html|title=Programming in D - Universal Function Call Syntax (UFCS)|website=Ddili.org|accessdate=1 October 2017}}</ref> (behaving similar to [[Pipe (computer science)|pipe]]s, or the various dedicated [[Operator (computer programming)|operator]]s available in [[functional language]]s for passing values through a series of [[Expression (computer science)|expression]]s). It allows free-functions to fill a role similar to [[extension method]]s in some other languages. Another benefit of the method call syntax is use with "[[dot-autocomplete]]" in [[IDE (computing)|IDE]]s, which use type information to show a list of available functions, dependent on the context. When the programmer starts with an argument, the set of potentially applicable functions is greatly narrowed down,<ref name="auto">{{cite web|title="Unified Call Syntax"|url=https://isocpp.org/files/papers/N4165.pdf|format=PDF|website=Isocpp.org|accessdate=1 October 2017}}</ref> aiding [[discoverability]].
Proposals for a unification of member function and free function calling syntax have been discussed from the early years of C++ standardization. Glassborow (2004) proposed a Uniform Calling Syntax (UCS), allowing specially annotated free functions to be called with member function notation.<ref>{{cite web|title=N1585: Uniform Calling Syntax (Re-opening public interfaces)|author=Francis Glassborow|date=2 May 2004|url=http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2004/n1585.pdf|accessdate=17 December 2018}}</ref>▼
It has more recently been proposed (as of 2016) for addition to C++ by [[Bjarne Stroustrup]]<ref>{{cite web|title="UFCS proposal"|url=http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4174.pdf|format=PDF|website=Open-std.org|accessdate=1 October 2017}}</ref> and [[Herb Sutter]],<ref name="auto"/> to reduce the ambiguous decision between writing [[free function (c++)|free function]]s and member functions, to simplify the writing of [[generic programming|templated code]]. Many programmers are tempted to write member functions to get the benefits of the member function syntax (e.g. "[[dot-autocomplete]]" to list [[member function]]s);<ref>{{cite web|title=using intellisense|url=https://msdn.microsoft.com/en-us/library/hcw1s69b.aspx|website=Msdn.microsoft.com|accessdate=1 October 2017}}</ref> however, this leads to excessive [[Coupling (computer programming)|coupling]] between [[Class (computer programming)|classes]].<ref>{{cite web|title=How Non-Member Functions improve encapsulation|url=https://www.drdobbs.com/cpp/how-non-member-functions-improve-encapsu/184401197|website=Drdobbs.com|accessdate=1 October 2017}}</ref>▼
== Examples ==
=== Nim programming language ===
<syntaxhighlight lang="Nim">▼
type Vector = tuple[x, y: int]▼
proc add(a, b: Vector): Vector =▼
(a.x + b.x, a.y + b.y)▼
let▼
v1 = (x: -1, y: 4)▼
v2 = (x: 5, y: -2)▼
v3 = add(v1, v2)▼
v4 = v1.add(v2)▼
v5 = v1.add(v2).add(v1)▼
</syntaxhighlight>▼
=== D programming language ===
<syntaxhighlight lang="D">
Line 39 ⟶ 51:
</syntaxhighlight>
▲Proposals for a unification of member function and free function calling syntax have been discussed from the early years of C++ standardization. Glassborow (2004) proposed a Uniform Calling Syntax (UCS), allowing specially annotated free functions to be called with member function notation.<ref>{{cite web|title=N1585: Uniform Calling Syntax (Re-opening public interfaces)|author=Francis Glassborow|date=2 May 2004|url=http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2004/n1585.pdf|accessdate=17 December 2018}}</ref>
▲<syntaxhighlight lang="Nim">
▲It has more recently been proposed (as of 2016) for addition to C++ by [[Bjarne Stroustrup]]<ref>{{cite web|title="UFCS proposal"|url=http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4174.pdf|format=PDF|website=Open-std.org|accessdate=1 October 2017}}</ref> and [[Herb Sutter]],<ref name="auto"/> to reduce the ambiguous decision between writing [[free function (c++)|free function]]s and member functions, to simplify the writing of [[generic programming|templated code]]. Many programmers are tempted to write member functions to get the benefits of the member function syntax (e.g. "[[dot-autocomplete]]" to list [[member function]]s);<ref>{{cite web|title=using intellisense|url=https://msdn.microsoft.com/en-us/library/hcw1s69b.aspx|website=Msdn.microsoft.com|accessdate=1 October 2017}}</ref> however, this leads to excessive [[Coupling (computer programming)|coupling]] between [[Class (computer programming)|classes]].<ref>{{cite web|title=How Non-Member Functions improve encapsulation|url=https://www.drdobbs.com/cpp/how-non-member-functions-improve-encapsu/184401197|website=Drdobbs.com|accessdate=1 October 2017}}</ref>
▲type Vector = tuple[x, y: int]
▲proc add(a, b: Vector): Vector =
▲ (a.x + b.x, a.y + b.y)
▲let
▲ v1 = (x: -1, y: 4)
▲ v2 = (x: 5, y: -2)
▲ v3 = add(v1, v2)
▲ v4 = v1.add(v2)
▲ v5 = v1.add(v2).add(v1)
▲</syntaxhighlight>
== Rust usage of the term ==
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