Struct Substituter

Source

pub struct Substituter<'a> { /* private fields */ }

Expand description

Performs value substitution on a string value.

Supports {{VAR_NAME}} syntax. Escaping is supported via \{\{ and \}\}. Values are looked up via a ValueResolver — EnvValueResolver by default, backed by std::env::var.

Used by real, technology-specific LoaderOps implementors (see configbuilder-svc-loader-spi) to apply substitution after parsing a config file.

Implementations§

Source §

impl<'a> Substituter<'a>

Source

pub fn new( policy: &'a dyn SubstitutionPolicy, resolver: &'a dyn ValueResolver, location: String, ) -> Self

Create a new substituter with a policy and value resolver.

Examples found in repository ?

examples/prefix_whitelist.rs (line 12)

6fn main() {
7    // SAFETY: single-threaded example, no concurrent env access.
8    unsafe { std::env::set_var("APP_HOST", "example.internal") };
9
10    let policy = PrefixWhitelistPolicy::new(vec!["APP_".to_string()]);
11    let resolver = EnvValueResolver;
12    let substituter = Substituter::new(&policy, &resolver, "example.toml".to_string());
13
14    match substituter.substitute("host = {{APP_HOST}}") {
15        Ok(value) => println!("{value}"),
16        Err(e) => eprintln!("substitution failed: {e}"),
17    }
18}

Source

pub fn substitute(&self, value: &str) -> Result<String, SubstitutionError>

Substitute all {{VAR_NAME}} placeholders in the given value.

§Returns

Ok(substituted_value) if substitution succeeds
Err(SubstitutionError) if:
- A referenced variable doesn’t exist
- A variable is rejected by the policy
- The syntax is invalid (e.g., nested placeholders)

Examples found in repository ?

examples/prefix_whitelist.rs (line 14)

6fn main() {
7    // SAFETY: single-threaded example, no concurrent env access.
8    unsafe { std::env::set_var("APP_HOST", "example.internal") };
9
10    let policy = PrefixWhitelistPolicy::new(vec!["APP_".to_string()]);
11    let resolver = EnvValueResolver;
12    let substituter = Substituter::new(&policy, &resolver, "example.toml".to_string());
13
14    match substituter.substitute("host = {{APP_HOST}}") {
15        Ok(value) => println!("{value}"),
16        Err(e) => eprintln!("substitution failed: {e}"),
17    }
18}