Interpolation
Interpolation is the construction of text by inserting evaluated values or expressions into designated placeholders in a string or template.
The Well-Grounded Rubyist, Fourth Edition
String interpolation is the Ruby language feature that evaluates embedded expressions and inserts their results into a string or regular expression.
- How it is used
- Places evaluated values into formatted output and inserts strings into regexp patterns.
- How deep it goes
- Explains expression evaluation, quoting controls, and regexp escaping through worked examples, without descending into implementation internals.
- Examples
- Uses ticket output, arithmetic in differently quoted strings, and a dot-containing regexp that matches too broadly.
- What you can do after
- Apply it to format Ruby strings and interpolate literal text safely into regexps with Regexp.escape.
Read how The Well-Grounded Rubyist, Fourth Edition explains interpolation →
Get Programming with JavaScript Next: New features of ECMAScript 2015, 2016, and beyond
The insertion of a value into a string’s text during string construction so the value becomes part of the resulting string.
- How it is used
- Builds strings containing dynamic values, including messages and generated HTML.
- How deep it goes
- Shows `${...}` expressions and contrasts interpolation with concatenation, without detailing evaluation internals.
- Examples
- Uses cart counts, greetings, mad libs, prices, and product HTML.
- What you can do after
- Build it from scratch: construct strings with dynamic values using template literals instead of concatenation.
Tiny CSS Projects
Sass interpolation evaluates an expression and inserts its result into generated CSS text, such as selectors, property names, or values.
- How it is used
- Uses Sass expressions to generate dynamic CSS property names, selectors, and content.
- How deep it goes
- Defines the hash-and-braces syntax and demonstrates compilation, but does not descend into Sass implementation internals.
- Examples
- Shows a dynamic margin declaration and generated success, warning, and error callout classes and labels.
- What you can do after
- Apply it via Sass to construct CSS names and text from variables while generating repeated rules from maps.
Python How-To
String interpolation is the insertion of variable or expression values into a string template to produce textual output.
- How it is used
- Uses interpolation to prepare readable output from existing variables and values of different types.
- How deep it goes
- Explains f-string syntax, supported values, older alternatives, and escaped braces without descending into implementation internals.
- Examples
- Demonstrates task labels, collections, dictionaries, assertions, and price-tag braces requiring escaped interpolation markers.
- What you can do after
- Apply it via Python f-strings to build readable output from strings, numbers, collections, and other values.
Related concepts
- to_sused by · to_s is a Ruby conversion method that returns a string representation of its receiver.
- template literalused by · A JavaScript string literal delimited by backticks that supports multiline text and embedded expressions.
- f-stringimplemented by · An f-string is a Python formatted string literal that evaluates embedded expressions and inserts their formatted values into the resulting string.
- single-quoted stringcontrasts with · A single-quoted string is a string literal delimited by single quotation marks, with language-defined rules for escapes and interpolation.
- regular expressionuses · A formal pattern notation that describes sets of strings and enables text to be matched, searched, extracted, or transformed.
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