Uniform function call syntax: Difference between revisions

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{{Short description|Programming language feature}}

{{Primary sources|date=September 2017}}

'''Uniform Functionfunction Callcall Syntaxsyntax''' ('''UFCS''') or '''Uniformuniform Callingcall Syntaxsyntax''' ('''UCS''') or sometimes '''Universal Function Call Syntax''' is a [[programming language]] feature in [[D (programming language)|D]],<ref andname=":0" /> [[Nim (programming language)|Nim]],<ref>{{Cite web |title=Nim by Example - Procs |url=https://nim-by-example.github.io/procs/ |access-date=2024-05-19 |website=nim-by-example.github.io}}</ref> Koka,<ref>{{Cite web |title=The Koka Programming Language |url=https://koka-lang.github.io/koka/doc/book.html |access-date=2024-05-19 |website=koka-lang.github.io}}</ref> and Effekt<ref>{{Cite web |title=Functions |url=https://effekt-lang.org/tour/functions |access-date=2025-04-09 |website=Effekt Language}}</ref> 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 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 - |website=D Programming Language|website=Dlang.org |accessdate=1 October 2017}}</ref> The same technique is used in the [[AviSynth]] scripting language under the name "OOP notation".<ref>{{cite web |title=Operators - |website=Avisynth wiki |url=http://avisynth.nl/index.php/Operators#Operator_Precedence |quote=<code>a.function(b)</code> is equivalent to <code>function(a, b)</code>}}</ref>

UFCS is particularly useful when function calls are chained<ref name=":0">{{cite web |url=http://ddili.org/ders/d.en/ufcs.html |title=Programming in D - Universal Function Call Syntax (UFCS) |website=Ddili.orgProgramming in D |accessdate=1 October 2017}}</ref> (behaving similar to [[Pipe (computer science)|pipepipes]]s, or the various dedicated [[Operator (computer programming)|operatoroperators]]s available in [[functional language]]s for passing values through a series of [[Expression (computer science)|expressionexpressions]]s). It allows free- functions to fill a role similar to [[extension method]]s in some other languages. Another benefit of the syntax is related to completion systems in [[Integrated development environment|IDEs]], 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]].

== Examples ==

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// all the following are correct and equivalent

int b = first(a);

int c = a.first();

int d = a.first;

// chaining

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== C++ proposal ==

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 Uniformuniform Callingcalling Syntaxsyntax (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>

In 2016 it has beenwas proposed a second time 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 functionFunction (ccomputer programming)#C and C++)|free functionfunctions]]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. "[[Code completion|dot-autocomplete]]" to list [[member function]]s);<ref>{{cite web |title=usingUsing IntelliSense intellisense|url=https://msdn.microsoft.com/en-us/library/hcw1s69b.aspx |website=Msdn.microsoft.comMSDN |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 improveImprove Encapsulation encapsulation|url=https://www.drdobbs.com/cpp/how-non-member-functions-improve-encapsu/184401197 |website=Drdobbs.com |accessdate=1 October 2017}}</ref> This was again, in 2023, proposed by Herb Sutter<ref>{{Cite web |last=Sutter |first=Herb |date=13 October 2023 |title=Unified function call syntax (UFCS) |url=https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p3021r0.pdf }}</ref> claiming new information and insights, as well as an experimental implementation in the cppfront compiler.

== Rust usage of the term ==

Until 2018, it was common<ref>{{Cite web |title=Rename UFCS to accurately reflect its functionality. · Issue #1140 · rust-lang/rfcs |url=https://github.com/rust-lang/rfcs/issues/1140 |access-date=2024-05-19 |website=GitHub |language=en}}</ref> to use this term when actually referring to ''[https://github.com/rust-lang/rfcs/issues/1140#issuecomment-108644620 qualified/explicit path syntax]'' and most commonly the ''[https://doc.rust-lang.org/1.30.0/book/2018-edition/ch19-03-advanced-traits.html?highlight=trait,function,call#fully-qualified-syntax-for-disambiguation-calling-methods-with-the-same-name Fullyfully Qualifiedqualified Pathpath syntax].'': because it's is possible to have several traits defining the same method implemented on the same struct, a mechanism is needed to disambiguate which trait should be used. Member functions can also be used as free functions through a qualified (namespaced) path. The term UFCS is incorrect for these uses, as it allows using methods as (namespaced) free functions, but not using free functions as methods.

Member functions can also be used as free functions through a qualified (namespaced) path.

The term UFCS is incorrect for these uses, as it allows using methods as (namespaced) free functions, but not using free functions as methods.

== See also ==