Type assertion

As explained in Build and Orchestrator in Go (From Scratch)

A type assertion is a Go operation that extracts a value of a specified concrete or interface type from an interface value.

How Build and Orchestrator in Go (From Scratch) covers it

How deep it goes

Explains the two-result assertion, its ok check, and failure handling, but does not descend into runtime representation internals.

Examples

Demonstrates assertions while storing, retrieving, updating, listing, and processing task and task-event values.

What it assumes

Assumes familiarity with Go interfaces, pointers, methods, and error returns while demonstrating interface-to-concrete conversion in context.

What you can do after

Diagnose/debug with it by checking ok and returned errors before using an interface value as its expected concrete type.

How it connects

Connects type assertions with interfaces, empty interfaces, pointers, comma-ok checks, error handling, and in-memory stores.

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Also explained in

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  liveBookmanning.com
  Go by ExampleA runtime type assertion is a Go expression that checks and retrieves the concrete value represented by an interface value at run time.
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  liveBookmanning.com
  Essential TypeScript 5, Third EditionA type assertion is a TypeScript construct that tells the compiler to treat an expression as a specified type without performing a runtime type conversion.
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  liveBookmanning.com
  Go in Action, Second EditionA type assertion is a Go operation that checks whether an interface value contains a specified concrete type and retrieves the contained value if it does.
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  liveBookmanning.com
  Go in Practice, Second EditionA type assertion is a Go operation that retrieves the concrete value of an interface value when it has a specified dynamic type.

Compare how 5 books explain type assertion →

Related concepts

• reflectionalternative to · Reflection is a programming capability for inspecting or interacting with program types, members, values, or metadata dynamically at runtime.
• typeof operatoralternative to · A typeof operator obtains type information about an operand or expression, yielding a type or a string describing its type depending on the language.
• as operatoruses · The as operator is language syntax that associates a value or expression with a specified type through assertion, casting, or conversion, depending on the language.
• sql.DBused by · sql.DB is a Go database/sql handle that provides database operations while managing a pool of database connections.
• any typeuses · The any type is a TypeScript type that permits values to be treated as having essentially any type, largely disabling static type checking for them.
• data conversioncontrasts with · Data conversion is the transformation of a value or data from one type, format, or representation to another, explicitly or implicitly.

This explainer was generated by Manning's knowledge graph from the text of Build and Orchestrator in Go (From Scratch). The section links point to the parts of the book it draws on.