Module core.interpolation
This module provides definitions to support D's interpolated expression sequence literal, sometimes called string interpolation.
string str;
int num;
// the compiler uses this module to implement the
// i"..." literal used here.
auto a = i"$(str) has $(num) items."; The variable a is a sequence of expressions:
a[0] == InterpolationHeader()
a[$-1] == InterpolationFooter()First and last, you see the header and footer, to clearly indicate where interpolation begins and ends. Note that there may be nested interpolated sequences too, each with their own header and footer. Think of them as a set of balanced parenthesis around the contents.
Inside, you will find three general categories of
content
InterpolatedLiteral!"string" for string
expressions, InterpolatedExpression!"code" for code
expressions, and then the values themselves as their
own type.
In the example:
auto a = i"$(str) has $(num) items.";We will find:
a[0] == InterpolationHeader()
a[1] == InterpolatedExpression!"str"
a[2] == str
a[3] == InterpolatedLiteral!" has ";
a[4] == InterpolatedExpression!"num";
a[5] == num
a[6] == InterpolatedLiteral!" items.";
a[7] == InterpolationFooter()
aYou can see the correspondence with the original
input
when you write $(expression), the string of the
expression is passed as InterpolatedExpression!ThatString,
(excluding any parenthesis around the expression),
and everything else is passed as InterpolatedLiteral!str,
in the same sequence as they appeared in the source.
After an InterpolatedExpression!..., you will find the
actual value(s) in the tuple. (If the expression expanded
to multiple values - for example, if it was itself a tuple,
there will be multiple values for a single expression.)
Library functions should NOT attempt to mixin the code
from an InterpolatedExpression themselves. Doing so
will fail, since it is coming from a different scope anyway.
The string is provided to you only for informational purposes
and as a sentinel to separate things the user wrote.
Your code should be able to handle an empty code string
in InterpolatedExpression or even an entirely missing
InterpolatedExpression, in case an implementation decides to
not emit these.
The toString members on these return null, except for
the InterpolatedLiteral, which returns the literal string.
This is to ease processing by generic functions like
write or text, making them effectively
transparently skipped.
To extract the string from an InterpolatedLiteral, you can
use an is expression or the
To extract the string from a InterpolatedExpression, you can
use an is expression or the
None of these structures have runtime state.
History
Added in dmd 2.10x frontend, released in late 2023.
Structs
| Name | Description |
|---|---|
InterpolatedExpression
|
Represents the source code of an expression passed as part of an interpolated expression sequence. |
InterpolatedLiteral
|
Represents a fragment of a string literal in between expressions passed as part of an interpolated expression sequence. |
InterpolationFooter
|
Sentinel values to indicate the beginning and end of an interpolated expression sequence. |
InterpolationHeader
|
Sentinel values to indicate the beginning and end of an interpolated expression sequence. |