rust / intermediate
Snippet
Custom Error Types with Display and std::error::Error
Custom error types encapsulate domain-specific failure modes. By implementing Display, errors become human-readable. The Error trait enables composability with Rust's ? operator and error propagation chains. This approach provides structured error handling beyond basic Result types.
snippet.rs
rust
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use std::fmt;use std::error::Error;#[derive(Debug)]enum DataStoreError {NotFound(String),PermissionDenied { resource: String, user: String },ConnectionFailed(String),}impl fmt::Display for DataStoreError {fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {match self {DataStoreError::NotFound(key) => write!(f, "Item '{}' not found", key),DataStoreError::PermissionDenied { resource, user } => {write!(f, "User '{}' cannot access '{}'", user, resource)},DataStoreError::ConnectionFailed(msg) => write!(f, "Connection failed: {}", msg),}}}impl Error for DataStoreError {}fn lookup_user(user_id: &str) -> Result<String, DataStoreError> {if user_id.is_empty() {return Err(DataStoreError::NotFound("empty user id".to_string()));}if user_id == "forbidden" {return Err(DataStoreError::PermissionDenied {resource: "user database".to_string(),user: user_id.to_string(),});}Ok(format!("User #{}", user_id))}fn main() {match lookup_user("forbidden") {Ok(name) => println!("Found: {}", name),Err(e) => eprintln!("Error: {}", e),}}
Breakdown
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enum DataStoreError {
Variants capture different failure scenarios with context-rich data
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PermissionDenied { resource: String, user: String }
Struct-like variant carries multiple contextual fields
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impl fmt::Display for DataStoreError {
Display impl enables human-readable error messages
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impl Error for DataStoreError {}
Error trait enables ? operator and error chaining in calling code
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Result<String, DataStoreError>
Function returns typed errors for caller to handle appropriately