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‎_sips/sips/interpolation-quote-escape.md

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---
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layout: sip
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title: SIP-37 - Quote escapes for interpolations
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stage: completed
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status: shipped
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permalink: /sips/:title.html
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redirect_from: /sips/pending/interpolation-quote-escape.html
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---
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> This proposal has been implemented in Scala 2.13.6 and Scala 3.0.0.
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**By: Martijn Hoekstra**
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## History
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| Date | Version |
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|---------------|-----------------------|
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| Jul 31th 2018 | Initial Draft |
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| Aug 1st 2018 | Process lead comments |
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| Nov 2nd 2019 | Link dotty impl |
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## Introduction
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It's not straight-forward how to have a quote character (`"`) in an
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interpolation. Parsing interpolations does not process backslash escapes, but
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rather passes the raw string to the interpolator, which then has the option to
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process escapes itself as it sees fit. That means there are no lexing rules that
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process the escape, and the sequence `\"` simply terminates the interpolation.
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Interpolations have a different meta-character -- the `$` character -- which is
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treated specially. Interpolations use this escape to splice in arguments, and it
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can also be used to escape itself as the sequence `$$` to represent a literal
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`$` character.
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Because of its special handling during the parse, the `$` could be used to
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escape a `"` character to represent a literal `"` withing a string.
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## Motivating Example
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That the `"` character can't be easily escaped in interpolations has been an
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open issue since at least 2012[^1], and how to deal with this issue is a
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somewhat common SO question[^2][^3]
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{% highlight Scala %}
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s"A common question for Scala programmers is "How can I represent a literal " character in Scala interpolations?""
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{% endhighlight %}
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Doesn't work.
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Neither does
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{% highlight Scala %}
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s"A common question for Scala programmers is \"How can I represent a literal \" character in Scala interpolations?\""
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{% endhighlight %}
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### Examples
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{% highlight Scala %}
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s"A common question for Scala programmers is $"How can I represent a literal $" character in Scala interpolations?$""
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{% endhighlight %}
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### Comparison Examples
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There are a number of ways to work around the current restriction.
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The simplest is triple-quoting the interpolation:
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{% highlight Scala %}
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s"""A common question for Scala programmers is "How can I represent a literal " character in Scala interpolations?""""
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{% endhighlight %}
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Another common workaround is splicing in a separate string in one way or another.
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{% highlight Scala %}
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//with a normal escape in a string in a block
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s"A common question for Scala programmers is ${"\""}How can I represent a literal ${"\""} character in Scala interpolations?${"\""}"
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//with a quote character as a block
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s"A common question for Scala programmers is ${'"'}How can I represent a literal ${'"'} character in Scala interpolations?${'"'}"
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//with an identifier referencing a string that contains a single quote
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val quote = "\""
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s"A common question for Scala programmers is ${q}How can I represent a literal $q character in Scala interpolations?$q"
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{% endhighlight %}
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The second set of workarounds is dependent on the actual interpolator, and the
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quote becomes an argument. The `s`, `f` and `raw` interpolators splice their
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arguments in to the string, as is the obvious use and implementation of an
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interpolator. But it's not the only possible use and implementation for an
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interpolator and this way of inserting quotes may not work for any given
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interpolator.
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## Design
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This is a non-breaking change. Currently the sequence `$"` within an
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interpolation is a syntax error, as has already been noted[^4]
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on the original ticket.
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## Implementation
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The implementation is simple to the point of being trivial: see
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the implementation [^5] for the actual change in functionality and the rest of
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that PR for the spec and test changes.
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There is also an implementation for Dotty.[^7]
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## Drawbacks
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Adding this feature makes the language just a bit more irregular. There already
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is some amount of irregularity around string literals and interpolations in
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the language. An argument could be made that this change makes that worse rather
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than better.
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Because it affects parsing, this change may affect syntax highlighters. Syntax
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highlighters tend to already struggle around "funky" strings and interpolations.
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## Alternatives
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More ambitious proposals around interpolations are possible, and have been
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proposed in different forms before. For example, there was a PR thatshows more options
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around using `\` as a meta character in interpolations[^6]. It stranded somewhere
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between red tape, ambition and changing processes.
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I suspect the last word about interpolations hasn't been spoken, and that later
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proposals may still make interpolations more regular. This proposal is
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deliberately small, and intends not to be in the way of any potential further
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proposals.
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[^1]: https://github.com/Scala/bug/issues/6476 "\\\" escape does not work with string interpolation"
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[^2]: https://stackoverflow.com/questions/31366563/string-interpolation-escaping-quotation-mark/31366588 ""
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[^3]: https://stackoverflow.com/questions/17085354/escaping-quotation-marks-in-f-string-interpolation ""
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[^4]: https://github.com/scala/bug/issues/6476#issuecomment-292412577 "@retronym said: +1 to s"$"". Because it doesn't compile today, we don't risk changing the meaning of existing programs."
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[^5]: https://github.com/Scala/Scala/pull/6953/files#diff-0023b3bfa053fb16603156b785efa7ad ""
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[^6]: https://github.com/Scala/Scala/pull/4308 "SI-6476 Accept escaped quotes in interp strings"
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[^7]: https://github.com/lampepfl/dotty/pull/7486 "PR in dotty"
1+
---
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layout: sip
3+
title: SIP-37 - Quote escapes for interpolations
4+
stage: completed
5+
status: shipped
6+
permalink: /sips/:title.html
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redirect_from: /sips/pending/interpolation-quote-escape.html
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---
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10+
> This proposal has been implemented in Scala 2.13.6 and Scala 3.0.0.
11+
12+
**By: Martijn Hoekstra**
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## History
15+
16+
| Date | Version |
17+
|---------------|-----------------------|
18+
| Jul 31th 2018 | Initial Draft |
19+
| Aug 1st 2018 | Process lead comments |
20+
| Nov 2nd 2019 | Link dotty impl |
21+
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## Introduction
23+
24+
It's not straight-forward how to have a quote character (`"`) in an
25+
interpolation. Parsing interpolations does not process backslash escapes, but
26+
rather passes the raw string to the interpolator, which then has the option to
27+
process escapes itself as it sees fit. That means there are no lexing rules that
28+
process the escape, and the sequence `\"` simply terminates the interpolation.
29+
30+
Interpolations have a different meta-character -- the `$` character -- which is
31+
treated specially. Interpolations use this escape to splice in arguments, and it
32+
can also be used to escape itself as the sequence `$$` to represent a literal
33+
`$` character.
34+
35+
Because of its special handling during the parse, the `$` could be used to
36+
escape a `"` character to represent a literal `"` withing a string.
37+
38+
## Motivating Example
39+
40+
That the `"` character can't be easily escaped in interpolations has been an
41+
open issue since at least 2012[^1], and how to deal with this issue is a
42+
somewhat common SO question[^2][^3]
43+
44+
{% highlight Scala %}
45+
s"A common question for Scala programmers is "How can I represent a literal " character in Scala interpolations?""
46+
{% endhighlight %}
47+
48+
Doesn't work.
49+
50+
Neither does
51+
52+
{% highlight Scala %}
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s"A common question for Scala programmers is \"How can I represent a literal \" character in Scala interpolations?\""
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{% endhighlight %}
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### Examples
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{% highlight Scala %}
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s"A common question for Scala programmers is $"How can I represent a literal $" character in Scala interpolations?$""
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{% endhighlight %}
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### Comparison Examples
63+
64+
There are a number of ways to work around the current restriction.
65+
66+
The simplest is triple-quoting the interpolation:
67+
{% highlight Scala %}
68+
s"""A common question for Scala programmers is "How can I represent a literal " character in Scala interpolations?""""
69+
{% endhighlight %}
70+
71+
Another common workaround is splicing in a separate string in one way or another.
72+
73+
{% highlight Scala %}
74+
//with a normal escape in a string in a block
75+
s"A common question for Scala programmers is ${"\""}How can I represent a literal ${"\""} character in Scala interpolations?${"\""}"
76+
//with a quote character as a block
77+
s"A common question for Scala programmers is ${'"'}How can I represent a literal ${'"'} character in Scala interpolations?${'"'}"
78+
//with an identifier referencing a string that contains a single quote
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val quote = "\""
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s"A common question for Scala programmers is ${q}How can I represent a literal $q character in Scala interpolations?$q"
81+
{% endhighlight %}
82+
83+
The second set of workarounds is dependent on the actual interpolator, and the
84+
quote becomes an argument. The `s`, `f` and `raw` interpolators splice their
85+
arguments in to the string, as is the obvious use and implementation of an
86+
interpolator. But it's not the only possible use and implementation for an
87+
interpolator and this way of inserting quotes may not work for any given
88+
interpolator.
89+
90+
## Design
91+
92+
This is a non-breaking change. Currently the sequence `$"` within an
93+
interpolation is a syntax error, as has already been noted[^4]
94+
on the original ticket.
95+
96+
## Implementation
97+
98+
The implementation is simple to the point of being trivial: see
99+
the implementation [^5] for the actual change in functionality and the rest of
100+
that PR for the spec and test changes.
101+
102+
There is also an implementation for Dotty.[^7]
103+
104+
## Drawbacks
105+
106+
Adding this feature makes the language just a bit more irregular. There already
107+
is some amount of irregularity around string literals and interpolations in
108+
the language. An argument could be made that this change makes that worse rather
109+
than better.
110+
111+
Because it affects parsing, this change may affect syntax highlighters. Syntax
112+
highlighters tend to already struggle around "funky" strings and interpolations.
113+
114+
## Alternatives
115+
116+
More ambitious proposals around interpolations are possible, and have been
117+
proposed in different forms before. For example, there was a PR thatshows more options
118+
around using `\` as a meta character in interpolations[^6]. It stranded somewhere
119+
between red tape, ambition and changing processes.
120+
121+
I suspect the last word about interpolations hasn't been spoken, and that later
122+
proposals may still make interpolations more regular. This proposal is
123+
deliberately small, and intends not to be in the way of any potential further
124+
proposals.
125+
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[^1]: https://github.com/Scala/bug/issues/6476 "\\\" escape does not work with string interpolation"
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[^2]: https://stackoverflow.com/questions/31366563/string-interpolation-escaping-quotation-mark/31366588 ""
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[^3]: https://stackoverflow.com/questions/17085354/escaping-quotation-marks-in-f-string-interpolation ""
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[^4]: https://github.com/scala/bug/issues/6476#issuecomment-292412577 "@retronym said: +1 to s"$"". Because it doesn't compile today, we don't risk changing the meaning of existing programs."
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[^5]: https://github.com/Scala/Scala/pull/6953/files#diff-0023b3bfa053fb16603156b785efa7ad ""
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[^6]: https://github.com/Scala/Scala/pull/4308 "SI-6476 Accept escaped quotes in interp strings"
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[^7]: https://github.com/lampepfl/dotty/pull/7486 "PR in dotty"

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