rust / intermediate
Snippet
Custom Error Types Implementing std::error::Error
Implementing the Error trait for custom error types creates idiomatic error handling in Rust. The Error trait requires Display implementation and provides std::error::Error compatibility for propagation with the ? operator. This pattern enables structured error handling with domain-specific error variants.
snippet.rs
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use std::fmt;use std::error::Error;#[derive(Debug)]enum ValidationError {EmptyField(String),InvalidFormat { field: String, expected: String },}impl fmt::Display for ValidationError {fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {match self {ValidationError::EmptyField(field) => write!(f, "Field '{}' cannot be empty", field),ValidationError::InvalidFormat { field, expected } => {write!(f, "Field '{}' has invalid format. Expected: {}", field, expected)}}}}impl Error for ValidationError {}fn validate_input(value: &str, field_name: &str) -> Result<(), ValidationError> {if value.is_empty() {return Err(ValidationError::EmptyField(field_name.to_string()));}if !value.contains('@') && field_name == "email" {return Err(ValidationError::InvalidFormat {field: field_name.to_string(),expected: "valid email address".to_string(),});}Ok(())}fn main() {if let Err(e) = validate_input("", "username") {eprintln!("Validation failed: {}", e);}}
Breakdown
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use std::fmt
Import fmt module for Display trait implementation
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#[derive(Debug)]
Derive Debug for error formatting in debug output
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enum ValidationError { EmptyField(String), InvalidFormat {...} }
Define enum with variants for different error scenarios
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impl fmt::Display for ValidationError
Implement Display trait to format error messages as user-facing strings
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impl Error for ValidationError {}
Implement std::error::Error trait enabling ? operator and error propagation
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if let Err(e) = validate_input("", "username")
Pattern match on error result to handle validation failure