Imagine that you need to interpolate strings, but the template variables are not quite cheap to load (such as system resources, network request, etc). And since the template are user-provided, you can't know ahead of time which variables you would need to load. You would need a flexible string template library that doesn't require calculating all these variables upfront.
Instead of requiring a complete set of inputs (such as via a struct, a HashMap, or a JSON object) to be available, the templates from this crate would send queries (which would usually be the names of the variables) to a function (called "responder") to get the value of each query.
While this library provides a preset parser for a preset template syntax (called curly_braces) that works out-of-the-box, it is also flexible enough to allow advanced users to provide their own component parsers or even a whole new template parser.
Go to docs.rs.
This is the most basic usage. There are more in the documentation.
let system = lazy_template::simple_curly_braces();
let template = system.lazy_parse("{name} is a {age} years old {gender}");
let output = template
.to_string(|query| match query {
"name" => Ok("Alice"),
"age" => Ok("20"),
"gender" => Ok("girl"),
_ => Err(format!("Can't answer {query}")),
})
.unwrap();
assert_eq!(output, "Alice is a 20 years old girl");The query in the example above is merely a variable name, but not necessarily. In more advanced use cases, query could be an expression, a command, a network request, or request for some system resource that would take time to load.