Zero value
A zero value is the default, type-dependent value assigned when a variable, field, or newly allocated value has no explicit initial value.
Learn Go with Pocket-Sized Projects
A zero value is the default value assigned to a Go variable or returned for an absent or uninitialized value of its type.
- How it is used
- Uses zero values to handle missing map entries, count books, and reason about cache initialization.
- How deep it goes
- Explains zero values through map lookups and an uninitialized cache map, without developing rules for every Go type.
- Examples
- Shows an unsupported-language greeting, a book counter, cache methods, and an out-of-bounds image lookup.
- What you can do after
- Diagnose/debug with it when a missing key yields an empty value or a cache contains an uninitialized map.
Read how Learn Go with Pocket-Sized Projects explains zero value →
Go by Example
A zero value is the default value assigned to a Go variable when no explicit initializer is provided.
- How it is used
- Simplifies test environments and service types by removing unnecessary initialization before use.
- How deep it goes
- Explains practical zero-value design through builders, pointer nil panics, lazy map initialization, option ambiguity, and copying cautions.
- Examples
- Demonstrates testEnv with strings.Builder fields, nil pointer builders, and a Shortener that initializes its map on demand.
- What you can do after
- Apply zero-value-friendly type designs while handling nil maps, pointer initialization, ambiguous option defaults, and stateful-value copying.
100 C++ Mistakes and How to Avoid Them
A zero value is the type-dependent zero-initialized value assigned to an object or variable by a relevant initialization operation.
- How it is used
- Uses type-dependent zero values to initialize objects and mark moved-from exclusive resources as lacking ownership.
- How deep it goes
- Explains initialization forms, undefined behavior, class invariants, and sentinel selection, but does not formalize language-standard rules.
- Examples
- Demonstrates Person initialization, explicit member constructors, invalid ages, and resetting pointers or value resources after transfer.
- What you can do after
- Diagnose uninitialized members and choose zero or invalid values that preserve class invariants during resource transfer.
Read how 100 C++ Mistakes and How to Avoid Them explains zero value →
API Design Patterns
A zero value is the empty or numerically zero representation that a data format or type uses when no distinct null representation is available.
- How it is used
- Guides API field and default design when formats cannot represent null or missing primitive values.
- How deep it goes
- Explains Boolean, numeric, and map consequences, but defers numeric default handling to serialization design.
- Examples
- Uses ChatRoom permissions, allowChatbots, disallowChatbots, numeric zero, and empty-versus-null maps.
- What you can do after
- Evaluate API defaults for ambiguity, intentional zero values, predictable behavior, and future default changes.
Go in Action, Second Edition
A zero value is the default value assigned to a newly declared Go variable when no explicit initial value is provided.
- How it is used
- Uses default values to make declarations and map access immediately usable without mandatory initialization.
- How deep it goes
- Explains defaults and map behavior with runnable patterns, but defers other zero-value details to later treatment.
- Examples
- Demonstrates default integers, missing map entries, Boolean membership maps, and numeric word-count lookups.
- What you can do after
- Apply zero values in declarations and map lookups, and diagnose absent keys with two-value assignment.
Related concepts
- Mapproduced by · A map is an associative data structure that stores key-value pairs and supports retrieving values by key.
- named result parameterused by · A named result parameter is a Go function result parameter declared with an identifier that can be referenced within the function body and is initialized to its type's zero value.
- missing valuecontrasts with · A missing value is a marker or condition indicating that an expected data value or reference is absent, unavailable, unknown, or inapplicable.
- attributeconfigures · An attribute is a named property, value, or piece of information associated with an entity, object, or program element.
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