Uniform function call syntax: Difference between revisions

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{{Short description|Programming language feature}}

'''Uniform Functionfunction Callcall Syntaxsyntax''' ('''UFCS''') or '''Uniformuniform Callcall Syntaxsyntax''' ('''UCS''') or sometimes '''Universal Function Call Syntax''' is a [[programming language]] feature in [[D (programming language)|D]],<ref name=":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> [[Rust (programming language)|Rust]],<ref>{{Cite web |title=Call expressions - The Rust Reference |url=https://doc.rust-lang.org/reference/expressions/call-expr.html#disambiguating-function-calls |access-date=2024-09-22 |website=doc.rust-lang.org}}</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 |last= |first= |title=Effekt Language: Introduction to EffektFunctions |url=https://effekt-lang.org/docstour/#function-applicationfunctions |access-date=20242025-0504-1909 |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 |website=Isocpp.org |accessdate=1 October 2017}}</ref> aiding [[discoverability]].

== Examples ==

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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 |website=Open-std.org |accessdate=1 October 2017}}</ref> and [[Herb Sutter]],<ref name="auto"/> to reduce the ambiguous decision between writing [[Function (computer programming)#C and C++|free functions]] 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 haswas again, in 2023, been 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 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.

== See also ==