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option

option

§
(T 
type
)
:
switch T, nil  
[Contains abstract features]
option -- feature wrapping a value or nothing

option represents an optional value of type T

Type Parameters

Functions

absolute value
returns o if outcome is ok, otherwise return the outcome's own
error.
synonym for infix >>=
this switch as an equatable_switch
§
 => 
list switch.A  
[Inherited from  switch]
converts switch into a list of either a single element in case
switch.this.exists or `nil`otherwise
§
 => 
option switch.A  
[Inherited from  switch]
convert this switch to an option
§
 => 
outcome switch.A  
[Inherited from  switch]
convert this switch to an outcome
§
(e error)
 => 
outcome switch.A  
[Inherited from  switch]
convert this switch to an outcome
§
 => 
String  
[Redefinition of  switch.as_string]
converts option to a string

returns the result of $T for an option containing an instance
of T, alternatively returns $nil for an option that is nil.
monadic operator

Same as non-generic >>=, but also maps to a different type B.
§
 => 
Type  
[Inherited from  Any]
Get the dynamic type of this instance. For value instances `x`, this is
equal to `type_of x`, but for `x` with a `ref` type `x.dynamic_type` gives
the actual runtime type, while `type_of x` results in the static
compile-time type.

There is no dynamic type of a type instance since this would result in an
endless hierarchy of types. So for Type values, dynamic_type is redefined
to just return Type.type.
§
 => 
bool  
[Inherited from  switch]
Does this switch contain a value of type A?
§
 => 
switch.A  
[Inherited from  switch]
unwraps a switch that is known to contain a value

this can only be called in cases where it is known for sure that this switch
is not nil. A runtime error will be created otherwise.
§
(default Lazy switch.A)
 => 
switch.A  
[Inherited from  switch]
unwrap value or get default
not equals operator
modulo operator
exponentation operator
multiplication operator
addition operator
subtraction operator
division operator
lower or equal than operator
lower than operator
equals operator
greater or equal than operator
monadic operator

redefines:

§
(B 
type
, MB 
type
:monad (monad.infix >>=~.B) (monad.infix >>=~.MB), f Unary MB monad.A)
 => 
MB  
[Inherited from  monad]
  
[Abstract feature]
monadic operator to another monad

Apply f to elements of type A and wrap them in MB.
monadic operator for bool result, false for nil
greater than operator
Does this option contain no value of type T?
is zero
§
(MMA 
type
:monad monad.MA monad.join.MMA, a MMA)
 => 
monad.MA  
[Inherited from  monad]
  
[Abstract feature]
join operator
§
 => 
bool  
[Inherited from  switch]
Does this switch contain a value of type A?
if this switch is nil return the result of f
otherwise just return this switch.
§
(default Lazy switch.A)
 => 
switch.A  
[Inherited from  switch]
unwraps an switch if it exists, returns default value otherwise.
§
 => 
bool  
[Inherited from  switch]
short-hand postfix operator for '!exists'
§
 => 
bool  
[Inherited from  switch]
short-hand postfix operator for 'exists'
§
 => 
bool  
[Inherited from  switch]
short-hand prefix operator for '!exists'
§
 => 
String  
[Inherited from  Any]
convenience prefix operator to create a string from a value.

This permits usage of `$` as a prefix operator in a similar way both
inside and outside of constant strings: $x and "$x" will produce the
same string.
'prefix +' (identity)
'prefix -' (negation)
sign function resulting in `-1`/`0`/`+1` depending on whether `numeric.this`
is less than, equal or larger than zero
§
 => 
switch.A  
[Inherited from  switch]
value of a switch that is known to contain a value

This can only be called in cases where it is known for sure that this
switch is not a B. A runtime error will be created otherwise.
§
(default switch.A)
 => 
switch.A  
[Inherited from  switch]
value of a switch or default if switch contains B

Type Functions

§
 => 
String  
[Inherited from  Type]
string representation of this type to be used for debugging.

result has the form "Type of '<name>'", but this might change in the future

redefines:

§
 => 
Type  
[Inherited from  Type]
There is no dynamic type of a type instance since this would result in an
endless hierarchy of types, so dynamic_type is redefined to just return
Type.type here.

redefines:

§
(T 
type
)
 => 
bool  
[Inherited from  Type]
Is this type assignable to a type parameter with constraint `T`?

The result of this is a compile-time constant that can be used to specialize
code for a particular type.

is_of_integer_type(n T : numeric) => T : integer
say (is_of_integer_type 1234) # true
say (is_of_integer_type 3.14) # false

it is most useful in conjunction preconditions or `if` statements as in

pair(a,b T) is
same
pre T : property.equatable
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=>
a = b
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or

val(n T) is

# check if T is numeric, if so
# return true if n > zero,
# return nil if T is not numeric
#
more_than_zero option bool =>
if T : numeric then
n > T.zero
else
nil
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§
 => 
String  
[Inherited from  Type]
name of this type, including type parameters, e.g. 'option (list i32)'.
§
 => 
String  
[Inherited from  Type]
convenience prefix operator to create a string from a value.

This permits usage of `$` as a prefix operator in a similar way both
inside and outside of constant strings: $x and "$x" will produce the
same string.

NYI: Redefinition allows the type feature to be distinguished from its normal counterpart, see #3913

redefines:

§
(a monad.type.A)
 => 
monad.type.MA  
[Inherited from  monad]
  
[Abstract feature]
return function
§
(a choice.this.type (in type feature))
 => 
choice.this.type (in type feature)  
[Inherited from  choice]
explicitly tag value a to become choice
§
 => 
Type  
[Inherited from  Any]
Get a type as a value.

This is a feature with the effect equivalent to Fuzion's `expr.type` call tail.
It is recommended to use `expr.type` and not `expr.type_value`.

`type_value` is here to show how this can be implemented and to illustrate the
difference to `dynamic_type`.
0.093dev (2025-05-13 15:50:27 GIT hash 38f965e14265a6f3ba3f96f18ddedb79352428af built by fridi@fzen)