• Java

String s = "%s%s".formatted(a, b);

• Java

StringBuilder t = new StringBuilder(a);
Formatter f = new Formatter(t);
f.format("%s", b).flush();
String s = t.toString();

• Java

String s = a + b;

• Java

String s = a.concat(b);

• JS

const s = a + b;

• Elixir

s = a <> b

• Ada

S : constant String := A & B;

• Clojure

(def s (str a b))

• C++

std::string a{"Hello"};
std::string b{"world"};
auto s = a + b;

• C#

string s = a + b;

• C#

string s = String.Concat(a,b);

• Dart

var s = '$a$b';

• Dart

var s = a + b;

• Fortran

s = a // b

• Go

s := a + b

• Haskell

s = a <> b

• Haskell

s = a ++ b

• Kotlin

val s = a + b

• Lua

local s = a..b

• PHP

$s = $a.$b;

• Pascal

s := a + b;

• Perl

my $s = $a . $b;

• Python

s = a + b

• Python

s = f'{a}{b}'

• Ruby

s = a + b

• Rust

let s = a + b;

• Rust

let s = format!("{}{}", a, b);

• VB

s = a & b