swift - dynamicType of optional chaining not the same as assignment -

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optional chaining returns always optional value.

to reflect fact optional chaining can called on nil value, result of optional chaining call optional value, if property, method, or subscript querying returns nonoptional value.

the swift programming language

why heck in playground type not optional?

let stringoptempty: string? = "" stringoptempty?.isempty // true stringoptempty?.isempty.dynamictype // bool.type

but following code is

let isok = stringoptempty?.isempty.dynamictype isok.dynamictype // optional<bool.type>.type

tldr;

the playground sidebar/column dynamically resolve expressions in playground, values assigned variables (mutables/immutables) or "free-floating" non-assigned values.

your first example applies dynamictype value, resolve type of specific value (true.dynamictype: bool.type).

your second example, on other hand, applies dynamictype variable (an immutable, i'll use variable here differ value), must have concrete type, , hence resolve type can hold kind of wrapped values (true or false) nil (here, nil is, specifically, optional<bool.type>.none), no matter value variable holds. hence, dynamictype resolve optional<bool.type>.type in second example.

details

the value displayed in playground sidebar/column follows following display rules:

  • for assignment expression, value shown in sidebar value assigned, e.g.

    var = 4 // shows '4' = 2     // shows '2' let b: () = (a = 3)           /* shows '()': _value_ assigned 'b', _result_              of assignment 'a = 3', _side effect_ 'a'              assigned value '3'. */

  • for expression contains no assignment, value shown in sidebar the result of expression, e.g.

    true          // shows 'true' 1 > 3         // shows 'false' let c = 3 c             // shows '3' c.dynamictype // shows 'int.type'

in first example (lines 2-3), have no assignment, , playground dynamically resolve value(/result) of expression prior resolving dynamictype of value. since we're dealing optionals, value either value of wrapped type (in case, true), or value type specific .none. if playground shows e.g. result of let a: int? = nil nil in sidebar, value shown in fact not same .none (nil) let b: string = nil

  • for let a: int? = nil, value of a in fact optional<int.type>.none,
  • whereas let b: string? = nil, value of b optional<string.type>.none

with in mind, it's natural resolved dynamictype of non-nil value concrete wrapped type (in example, bool.type naturally type of true), whereas resolved dynamictype of nil value include both general optional , wrapped type information. 

struct foo {     let bar: bool = true }  var foo: foo? = foo()  /* .some<t> case (non-nil) */ foo?.bar             // true <-- _expression_ resolves (results in) _value_ 'true' foo?.bar.dynamictype // bool.type <-- dynamic type of _result of expression_ true.dynamictype     // bool.type <-- compare  /* .none case (nil) */ foo = nil foo?.bar.dynamictype // nil <-- _expression_ resolves _value_ 'optional<foo.type>.none' optional<foo.type>.none.dynamictype                      // optional<foo.type>.type <-- compare

now, if assign values variable, naturally variable must have concrete type. since value assign at runtime can either .none or .some<t>, type of variable must 1 can hold values of both these cases, hence, optional<t.type> (disregarding of whether variable holds nil or non-nil value). case you've shown in second example: dynamictype of variable (here, immutable, using variable differ value) isok type can hold both .none , .some<t>, no matter actual value of variable is, , hence dynamictype resolves type; optional<bool.type>.type.

wrapping expressions in parantheses escapes runtime introspection of swift playground?

interestingly, if expression wrapped in parantheses prior applying .dynamictype, playground sidebar resolves .dynamictype of wrapped expression type of expression, if actual value unknown. e.g., (...) in (...).dynamictype treated variable concrete type rather runtime-resolved value. 

/* .some case (non-nil) */ foo?.bar               // true (foo?.bar).dynamictype /* optional<bool>.type <-- if (...)                            _variable_ of unknown value         */  /* .none case (nil) */ foo = nil (foo?.bar).dynamictype /* optional<bool>.type <-- if (...)                            _variable_ of unknown value         */

we can further note lone expression wrapped in parantheses in playground not resolve @ (in sidebar). it's if escape sidebar:s runtime introspection if wrapping expressions in parantheses (which explain why dynamictype of expressions wrapped in parantheses resolve if playground cannot make use runtime information of these expressions)

var = 4 // shows '4' (a = 2)   // shows nothing; can't expand or details in sidebar

tbh, cannot explain why is, , categorize peculiarity of swift playground.


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