Dart: How to force string interpolation on a variable

Question

I have a variable that contains a string with interpolated variables. In the code below, that variable is template. When I pass this variable to generateString function, I want to apply string interpolation on it because the values which interpolated variables require are available in generateString function only.

void main() {
  String template = '<p>\${name}</p>';
  var res = generateString(template);
}

generateString(template) {
  var name = 'abc';
  print(template);
  return template;
}

The problem is when I am printing and returning template inside generateString fn, I am getting <p>${name}</p> instead of <p>abc</p>. Is there a way to explicitly tell the dart to so string interpolation?

I am new to Dart. I don't know if it is even possible to achieve or not. Please suggest how do I do this.

Edit: Based on the inputs from other users, I would like to make a clarification about the scenario presented. The value of template variable is not a string literal. I get that from UI as a user input. I have shown it here as a string literal for code simplicity. Also, please consider that name and template are not in the same scope in my scenario.

your template should be inside "generateString" and then pass a parameter "name". Right now your generateString does absolutely nothing more that return the exact same thing you passed as parameter. — Mariano Zorrilla, Nov 25 '20 at 15:43

score 5 · Accepted Answer · answered Nov 25 '20 at 18:14

5

The other answers so far are wrong.

String interpolation (looking for $, etc) happens only while compiling from the source code to the value in memory. If that string in turn also has a $, it's no longer special.

It's not possible to trigger interpolation past the original compilation step. You can write a templating system that would look for something like {{name}} in the value, and replace it with the current value of name.

answered Nov 25 '20 at 18:14

Randal Schwartz

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Thank you for explaining why string interpolating wasn't working in this scenario. – JessePinkman Nov 25 '20 at 18:43

score 3 · Answer 2 · answered Nov 25 '20 at 16:15

3

If you have the template and the variable in the same scope, it works as expected.

// evaluate variable inside ${}
var sport = 'basketball';
String template = 'I like <p>${sport}</p>';
print(template);

answered Nov 25 '20 at 16:15

encubos

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No, this isn't working: the template is being processed as a result of compilation. That's not what OP is looking for. – Randal Schwartz Nov 25 '20 at 22:44

score 2 · Answer 3 · answered Nov 25 '20 at 16:05

2

I didn't fully understand your question maybe this will help

void main() {
  print(generateString('abc')); //<p>abc</p>
}

generateString(String template) {
  return r"<p>" "$template" r"</p>";
}

answered Nov 25 '20 at 16:05

Mr Random

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What a god, doesn't anderstand the question and still answer it – Lenny4 Apr 27 '23 at 01:04

Teddichiiwa · Answer 4 · 2020-11-25T15:51:46.173

0

Walter White here.

You must define the variable name as global var, so it can "cook" the string for you

edited Nov 25 '20 at 15:51

answered Nov 25 '20 at 15:41

Teddichiiwa

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Dart: How to force string interpolation on a variable

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