• Prolog

set_all_elements_to_same_value(X, V) :-
    length(X, Length),
    length(FilledList, Length),
    maplist(=(V), FilledList, X).

• C++

x.fill(v);

• C#

Array.Fill(x, v);

• Fortran

x = v

• Go

func fill[T any](x []T, v T) {
	for i := range x {
		x[i] = v
	}
}

• Go

for i := range x {
	x[i] = v
}

• Java

fill(x, v);

• Pascal

for i := Low(x) to High(x) do x[i] := v;

• Perl

my @x = (undef) x $n; 

foreach (@x) { $_ = $v }

• Perl

my @x = ($v) x $n;

• Python

x[:] = [v] * len(x)

• Ruby

x.fill(v)

• Rust

x.fill(v);