cast

Example: Cast

These examples use the cast from to modifier option to modify fields before assignment: This lets you perform direct type assertion, conversion, expressions, function usage, and property usage with a matched field.

Example	Description
Assert	Use cast generator options to enable automatic type assertion.
Convert	Use cast function option modifiers to enable direct type conversion.
Depth	Use cast option modifier depth to change autocasting behavior.
Expression	Use cast option modifier expression to evaluate an expression.
Function	Use cast option modifier func() to call a function.
Property	Use cast option modifier .Property to reference a type property.

Modifiers

Copygen handles assignability of fields with identical field names and definitions by default. Enable Copygen type casting when you must match fields using identical field names, but different definitions: This option modifies the matcher to match fields using an automatic or provided modifier.

Typecasting is not a feature in the Go programming language.

Assertion

Type assertion provides access to an interface's underlying concrete values: This lets you use the underlying concrete type's fields and functions. Enabling type assertion in Copygen applies to the following cases.

• Assignment of objects to interfaces: interface = type.
• Assertion of interfaces into objects: type = interface.(type).

Conversion

Type conversion changes the type of an expression to the type specified by the conversion: This lets you convert types into other types. Enabling type conversion in Copygen enables type conversion at the specified depth.

For example, custom = custom(bool) represents a type conversion at a depth of one.

Expressions

An expression is a value: Multiple expressions can be used to create statements which perform operations. Copygen cast modifiers are copied directly from the option. So using literal expressions (i.e * 2), type functions (i.e .String()), and type properties (i.e .Property) is allowed.

For example, cast model.Type.Field domain.Type.Field * 2 results in the assignment model.Type.Field = domain.Type.Field * 2 upon a match of the fields.

Usage

There are multiple ways to enable Copygen type casting.

Generator Options

# Define how the matcher will work.
matcher:
  # Skip the matcher (default: false).
  skip: false

  # Control the matcher type cast behavior.
  cast:
    # Enable automatic casting (default: false).
    enabled: true
    
    # Set the maximum depth for automatic casting (default: 1)
    depth: 1  
    
    # Disable certain features of casting.
    disabled:

      # Disable assignment of objects to interfaces (default: false).
      assignObjectInterface: false

      # Disable assertion of interfaces to objects (default: false).
      assertInterfaceObject: false

      # Disable type conversion (default: false).
      convert: false

Function Option

Use the cast from to modifier function option to enable casting for the respective function. Regex is supported for from-fields. The modifier flag is optional.

• cast .* package.Type.Field
• cast models.Account.ID domain.Account.ID .String()

Option Modifier

Use the -cast modifier function option modifier to enable casting for the respective function option. The modifier flag is optional.

• automatch package.Type.Field -cast
• automatch models.User.* -cast 1
• map .* package.Type.Field -cast .String()
• map .* package.Type.Field -cast Convert()
• tag package.Type.Field key -cast .Property
• tag .* api -cast + 100

Behavior

The cast option is a modifier: It modifies the matching algorithm or assignment of fields. It can't be used to match fields in a direct manner (unlike automatch, map, and tag).

Copygen will perform automatic typecasting using type assertion or conversion at the specified depth level when a modifier is NOT provided. Otherwise, the definition of the provided modifier is evaluated to match fields.

For example, map .* package.Type.Field -cast .String() matches from-fields with the name Field (from package.Type.Field) and definition string (since .String() returns string) when depth is greater than 0.