17.2.7 String interpolation

The syntax for string literals is extended to support string interpolation.

Within an interpolated string literal, an arbitrary expression, when enclosed in { ... }, is expanded at run time into the result of calling 'Image on the result of evaluating the expression enclosed by the brace characters, unless it is already a string or a single character.

Here is an example of this feature where the expressions Name and X + Y will be evaluated and included in the string.

procedure Test_Interpolation is
   X    : Integer := 12;
   Y    : Integer := 15;
   Name : String := "Leo";
begin
   Put_Line (f"The name is {Name} and the sum is {X + Y}.");
end Test_Interpolation;

In addition, an escape character (\) is provided for inserting certain standard control characters (such as \t for tabulation or \n for newline) or to escape characters with special significance to the interpolated string syntax, namely ", {, },and \ itself.

escaped_charactermeaning
\aALERT
\bBACKSPACE
\fFORM FEED
\nLINE FEED
\rCARRIAGE RETURN
\tCHARACTER TABULATION
\vLINE TABULATION
\0NUL
\\\
\""
\{{
\}}

Note that, unlike normal string literals, doubled characters have no special significance. So to include a double-quote or a brace character in an interpolated string, they must be preceded by a \. For example:

Put_Line
  (f"X = {X} and Y = {Y} and X+Y = {X+Y};\n" &
   f" a double quote is \" and" &
   f" an open brace is \{");

Finally, a syntax is provided for creating multi-line string literals, without having to explicitly use an escape sequence such as \n. For example:

Put_Line
  (f"This is a multi-line"
    "string literal"
    "There is no ambiguity about how many"
    "spaces are included in each line");

Here is a link to the original RFC : ‘https://github.com/AdaCore/ada-spark-rfcs/blob/master/prototyped/rfc-string-interpolation.rst