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<div>Begin forwarded message:</div>
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<span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif; color:rgba(0, 0, 0, 1.0);"><b>From:
</b></span><span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif;">Jim Laskey <james.laskey@oracle.com><br>
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<span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif; color:rgba(0, 0, 0, 1.0);"><b>Subject:
</b></span><span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif;"><b>Re: Syntax question for JEP 430: String Templates</b><br>
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<span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif; color:rgba(0, 0, 0, 1.0);"><b>Date:
</b></span><span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif;">April 11, 2023 at 1:11:58 PM ADT<br>
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<span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif; color:rgba(0, 0, 0, 1.0);"><b>To:
</b></span><span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif;">Octavia Togami <octavia.togami@gmail.com><br>
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<span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif; color:rgba(0, 0, 0, 1.0);"><b>Cc:
</b></span><span style="font-family: -webkit-system-font, Helvetica Neue, Helvetica, sans-serif;">amber-spec-comments@openjdk.org<br>
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<pre style="white-space: pre-wrap;"><span style="font-family: Helvetica;">Octavia,</span></pre>
<pre style="white-space: pre-wrap;"><font face="Helvetica">
I’m assuming you want ${…} used because that’s what many other languages use (if that is not the reason, apologies). I would argue that it is an advantage for Java not to use what other languages use. More on that toward the end of this reply.
JEP 430 indicates why \{…} was chosen and I don’t think the reasoning is weakened by the processor expression prefix requirement.
- Backslash was chosen because the combination of \{ would not create compatibility issues with older Java source.
- Braces were chosen because it is less likely that braces would be used in an embedded expression (versus parentheses and brackets). Note that Swift uses \(…).
Using ${…} to indicate embedded expressions would create two distinct categories of quoted elements, that is, ${…} would be lexically different for strings versus templates. Sounds simple, but tools wouldn't know which way to tokenize the quoted element until the tool’s grammar detected the "processor dot template" context (and note that processor can be a complex expression). Since most tools separate scanning (lexicon, tokens) from parsing (grammar) this forces the tooling to provide some sort of feedback between the lexicon and grammar — gets messy.
Using \(…) makes it easy for javac to tokenize both strings and templates without feedback from the parser. Note that you would have to add a new escape sequence for $ if you want to use $ in the template.)
Other languages can support ${…} at the lexicon level because their strings were designed to support ${…} from the beginning or have simple ways to indicate that the quoted element needs to be treated differently — different quotes, tag prefix, … .
Back to what I stated at the beginning, I think that \{…} is an advantage for string templates in much the same way that triple quotes works for text blocks, \{…} doesn’t conflict with other languages. Java serves a polyglot universe, where it is not uncommon to embed other language source in a Java app. For example;
</font>
<font face="Consolas">Object result = JAVASCRIPT."""
let header = "Templates Literals";
let tags = ["template literals", "javascript", "es6"];
let html = `<h2>${header}</h2><ul>`;
for (const x of tags) {
html += `<li>${x}</li>`;
}
html += `</ul>`;
""";
</font>
<font face="Helvetica">or
</font>
<font face="Consolas">Object result = BASH."""
Recipient=”<a href="mailto:admin@example.com">admin@example.com</a>”
Subject=”Greeting”
Message=”Welcome to our site”
`mail -s ${Subject} ${Recipient} <<< ${Message}`
""";
</font><span style="font-family: Helvetica;"><br></span></pre>
<pre><span style="white-space: pre-wrap; font-family: Helvetica;">Though you would not have the advantage of embedded expressions, </span><font face="Helvetica"><span style="white-space: pre-wrap;">it is also possible to use ${…} for your own style of template. We assume existing template libraries will provide similar StringTemplate “bridging".</span></font></pre>
<pre><font face="Consolas">static final StringTemplate.Processor<StringTemplate, RuntimeException> MY_STYLE = st -> {
String text = st.interpolate();
Pattern p = Pattern.compile("\\$\\{(.*?)\\}");
Matcher m = p.matcher(text);
List<String> fragments = new ArrayList<>();
List<String> values = new ArrayList<>();
int last = 0;
while (m.find()) {
fragments.add(text.substring(last, m.start()));
values.add(m.group(1));
last = m.end();
}
fragments.add(text.substring(last));
return StringTemplate.of(fragments, values);
};
</font><span style="font-family: Consolas;"><br></span></pre>
<pre>public static void main(String[] args) {
StringTemplate mailer = MY_STYLE."""
Dear ${name},
This is to inform you that your ${package} will be
delivered on ${date}.
Respectfully,
Big Shop
""";
Map<Object, Object> data = Map.of(
"name", "Joan",
"package", "bicycle",
"date", "May 31"
);
System.out.println(StringTemplate.interpolate(
mailer.fragments(),
mailer.values().stream().map(data::get).toList()
));
}</pre>
<pre><span style="font-family: Consolas;">-----------------------------------------------------</span><font face="Consolas">
</font></pre>
<pre>Dear Joan,
This is to inform you that your bicycle will be
delivered on May 31.
Respectfully,
Big Shop
</pre>
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<pre><font face="Consolas">-----------------------------------------------------</font></pre>
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<pre><font face="Helvetica"><span style="white-space: pre-wrap;">Hope this frames a better understanding. </span></font></pre>
<pre style="white-space: pre-wrap;"><span style="font-family: Helvetica;">Cheers,</span></pre>
<pre><font face="Helvetica"><span style="white-space: pre-wrap;">— Jim</span></font></pre>
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