Uniform Function Call Syntax

<h2 id="examples">Examples</h2>
<h3>D programming language</h3>
int first(int[] arr)
{
    return arr[0];
}

int[] addone(int[] arr)
{
    int[] result;
    foreach (value; arr) {
        result ~= value + 1;
    }
    return result;
}

void main()
{
    auto a = [0, 1, 2, 3];

// all the following are correct and equivalent
    int b = first(a);
    int c = a.first;

// chaining
    int[] e = a.addone().addone();
}

<h3>Nim programming language</h3>
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)

# all the following are correct
  v3 = add(v1, v2)
  v4 = v1.add(v2)
  v5 = v1.add(v2).add(v4)

<h2 id="c-proposal">C++ proposal</h2>
<p>Proposals for a unification of member function and free function calling syntax have been discussed from the early years of <a href="/facts/C%2B%2B/Et0F2qn9">C++</a> standardization. Glassborow (2004) proposed a Uniform Calling Syntax (UCS), allowing specially annotated free functions to be called with member function notation.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a>
In 2016 it has been proposed a second time for addition to C++ by <a href="/facts/Bjarne_Stroustrup/Be1Yq6rn">Bjarne Stroustrup</a><a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> and <a href="/facts/Herb_Sutter/a6QCepTt">Herb Sutter</a>,<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a> to reduce the ambiguous decision between writing <a href="/facts/Function_(computer_programming)/9vFJrg0A">free functions</a> and member functions, to simplify the writing of <a href="/facts/Generic_programming/kqtqJk7p">templated code</a>. Many programmers are tempted to write member functions to get the benefits of the member function syntax (e.g. "dot-autocomplete" to list <a href="/facts/Member_function/8kAXxVYs">member functions</a>);<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> however, this leads to excessive <a href="/facts/Coupling_(computer_programming)/QEeSaXF3">coupling</a> between <a href="/facts/Class_(computer_programming)/zvzkSAtE">classes</a>.<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a> This has again, in 2023, been proposed by Herb Sutter<a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a> claiming new information and insights as well as an experimental implementation in the cppfront compiler.
</p>
<h2 id="rust-usage-of-the-term">Rust usage of the term</h2>
<p>Until 2018, it was common<a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a> to use this term when actually referring to <i><a href="https://github.com/rust-lang/rfcs/issues/1140#issuecomment-108644620">qualified/explicit path syntax</a></i> and most commonly the <i><a href="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">Fully Qualified Path syntax</a>:</i> 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.
</p>
<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/Trait_(computer_programming)/olRmTbFe">Trait (computer programming)</a></li>
<li><a href="/facts/Interface_(computer_programming)/jDMpXoLN">Interface (computer programming)</a></li>
<li><a href="/facts/Go_(programming_language)/oWlsmAFJ">Go (programming language)</a>, another language with a more open philosophy to methods</li>
<li><a href="/facts/Loose_coupling/uXRb4qBJ">Loose coupling</a></li>
<li><a href="/facts/Duck_typing/tcuo8Ywq">Duck typing</a></li>
<li><a href="/facts/Method_chaining/1yKJJ9MA">Method chaining</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>"Programming in D - Universal Function Call Syntax (UFCS)". Ddili.org. Retrieved 1 October 2017. <a href="http://ddili.org/ders/d.en/ufcs.html" target="_blank">http://ddili.org/ders/d.en/ufcs.html</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>"Nim by Example - Procs". nim-by-example.github.io. Retrieved 2024-05-19. <a href="https://nim-by-example.github.io/procs/" target="_blank">https://nim-by-example.github.io/procs/</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>"The Koka Programming Language". koka-lang.github.io. Retrieved 2024-05-19. <a href="https://koka-lang.github.io/koka/doc/book.html" target="_blank">https://koka-lang.github.io/koka/doc/book.html</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>"Effekt Language: Introduction to Effekt". Effekt Language. Retrieved 2024-05-19. <a href="https://effekt-lang.org/docs/#function-application" target="_blank">https://effekt-lang.org/docs/#function-application</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
<li id="fn:5"><p>"Functions - D Programming Language". Dlang.org. Retrieved 1 October 2017. <a href="http://dlang.org/function.html#pseudo-member" target="_blank">http://dlang.org/function.html#pseudo-member</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li>
<li id="fn:6"><p>"Operators - Avisynth wiki". a.function(b) is equivalent to function(a, b) <a href="http://avisynth.nl/index.php/Operators#Operator_Precedence" target="_blank">http://avisynth.nl/index.php/Operators#Operator_Precedence</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li>
<li id="fn:7"><p>"Programming in D - Universal Function Call Syntax (UFCS)". Ddili.org. Retrieved 1 October 2017. <a href="http://ddili.org/ders/d.en/ufcs.html" target="_blank">http://ddili.org/ders/d.en/ufcs.html</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li>
<li id="fn:8"><p>""Unified Call Syntax"" (PDF). Isocpp.org. Retrieved 1 October 2017. <a href="https://isocpp.org/files/papers/N4165.pdf" target="_blank">https://isocpp.org/files/papers/N4165.pdf</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li>
<li id="fn:9"><p>Francis Glassborow (2 May 2004). "N1585: Uniform Calling Syntax (Re-opening public interfaces)" (PDF). Retrieved 17 December 2018. <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2004/n1585.pdf" target="_blank">http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2004/n1585.pdf</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li>
<li id="fn:10"><p>""UFCS proposal"" (PDF). Open-std.org. Retrieved 1 October 2017. <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4174.pdf" target="_blank">http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4174.pdf</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li>
<li id="fn:11"><p>""Unified Call Syntax"" (PDF). Isocpp.org. Retrieved 1 October 2017. <a href="https://isocpp.org/files/papers/N4165.pdf" target="_blank">https://isocpp.org/files/papers/N4165.pdf</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li>
<li id="fn:12"><p>"using intellisense". Msdn.microsoft.com. Retrieved 1 October 2017. <a href="https://msdn.microsoft.com/en-us/library/hcw1s69b.aspx" target="_blank">https://msdn.microsoft.com/en-us/library/hcw1s69b.aspx</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li>
<li id="fn:13"><p>"How Non-Member Functions improve encapsulation". Drdobbs.com. Retrieved 1 October 2017. <a href="https://www.drdobbs.com/cpp/how-non-member-functions-improve-encapsu/184401197" target="_blank">https://www.drdobbs.com/cpp/how-non-member-functions-improve-encapsu/184401197</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li>
<li id="fn:14"><p>Sutter, Herb (13 October 2023). "Unified function call syntax (UFCS)" (PDF). <a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p3021r0.pdf" target="_blank">https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p3021r0.pdf</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></p></li>
<li id="fn:15"><p>"Rename UFCS to accurately reflect its functionality. · Issue #1140 · rust-lang/rfcs". GitHub. Retrieved 2024-05-19. <a href="https://github.com/rust-lang/rfcs/issues/1140" target="_blank">https://github.com/rust-lang/rfcs/issues/1140</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></p></li>
</ol>

Uniform Function Call Syntax open-in-new

Uniform Function Call Syntax