PingCAP Style Guide

Guide to writing idiomatic code at PingCAP and in the TiKV project.

Project maintained by pingcap Hosted on GitHub Pages — Theme by mattgraham


Prefer meaningful names to short names.


All names should be from English.

When a name is forbidden because it is a reserved word (e.g., type, crate), use an abbreviation (e.g., ty) or an underscore suffix (e.g., crate_). Use raw identifiers (e.g., r#type, r#crate) if necessary; e.g., you are working with generated code or code which interacts with data using identifier names (e.g., JSON or protobuf libraries).

Prefer using full words rather than abbreviations, e.g., diagnostic and expansion_config rather than diag and expn_cfg. It’s ok to use abbreviations where they are well-known and standard outside the codebase (e.g., in the Rust or database communities). E.g., ctx for ‘context’, cf for ‘column family’, or expr for expression. When in doubt, use the full name. Use acronyms where the acronym is standard, e.g., Sql rather than StandardQueryLanguage. Treat acronyms as words, e.g., GrpcType or grpc_variable, not GRPCType or g_r_p_c_variable/GRPC_variable. In particular, ‘TiKV’ should be capitalised as Tikv, e.g., TikvServer, not TiKVServer Treat contractions of multiple words as one word, e.g., Stdin rather than StdIn.

Where it is clear from the wider context, if is fine to use short (even single character) names for local variables with very narrow scope. Some examples:

// Argument to inline closure (`s`).
vec.iter().map(|s| s.len());

// Single line `match` arm (`e`).
match ... {
    Ok(_) => { ... }
    Err(e) => println!("Error: {}", e),

// Counter in `for` loop (`i`).
for (i, label) in labels.iter().enumerate() {

When interfacing with non-Rust code, prefer to use Rust conventions in the Rust code, rather than conventions from another language. This may mean that items in Rust and non-Rust code have different names, but the correlation should be clear. Where necessary, use aliases or wrappers to avoid using unconventional names for FFI items.

Generic type and lifetime parameters should usually have short (usually single letter) names, e.g., T and 'a. Use longer names for generics if there are multiple generics in scope and short names are confusing. Associated types should have descriptive names like any other type.

Method names

A primary constructor function should be called new. A new constructor may take values for all fields or provide some defaults. Secondary constructors (which usually customise more values than in new) should usually be prefixed with with_, e.g., with_capacity.

A conversion method which preserves the original and gives a reference to a different type should be called as_type where type is the type being converted into. E.g., as_str, not as_str_ref or get_str or str. Such a conversion should be very cheap, usually just a different view on the original.

A conversion method which consumes the original and gives an owned value should be called into_type. E.g., into_string. An into_type method should not clone any part of the original (unless it is very cheap, e.g., Copy types).

An expensive conversion method (e.g., one which clones the original) should be called to_type. E.g., to_string or to_str.

Where a smart pointer or other wrapper type has a method which consumes the wrapper and returns the inner type, the method should be called into_inner if it will never panic and unwrap if it might panic. Where the wrapper is not consumed and a reference is returned, use get. For other unwrapping methods, follow the naming conventions used by Box, Option, and Result.

The default method for iterating over the contents of a type should be called iter. A method for iteration which consumes the collection should be called into_iter, however, such a method should usually be in an implementation of IntoIterator.

Prefer not to use getter and setter methods, but if you do they should be called foo and set_foo (where foo is the name of the field), not get_foo. Method for checking the presence of a field should have an is_ or has_ prefix and return a bool.

When naming traits: “Prefer (transitive) verbs, nouns, and then adjectives; avoid grammatical suffixes (like -able)”. E.g., Copy, Send, Encode.

Variations of methods which have different ownership or mutability properties from the default, should use suffixes to distinguish the variations. E.g., foo for the default variation (whether that is owned or by-ref), foo_ref for a by-reference version, and foo_mut for a by-mutable-reference version. Don’t use multiple suffixes, e.g. foo_mut_ref.

In most cases mutability does not need to be reflected in method names. Where it is required to disambiguate between mutable and non-mutable return types, for example, use mut should be a prefix, not a suffix. E.g., as_mut_slice, not as_slice_mut.


Existing guidance:

<< Formatting | Comments >>