Try? for optional result in Swift - Step-by-Step Execution

Concept Flow - Try? for optional result

Call throwing function

↓

Try? catches error?

↓

Return value

↓

Use optional result

Try? calls a function that might throw an error. If no error, it returns the value wrapped as optional. If error, it returns nil.

Execution Sample

Swift

enum ParseError: Error {
  case invalidFormat
}

func parseInt(_ str: String) throws -> Int {
  if let num = Int(str) { return num }
  else { throw ParseError.invalidFormat }
}

let result = try? parseInt("123")

This code tries to convert a string to an integer. If it works, result is the number wrapped as optional. If it fails, result is nil.

Execution Table

Step	Action	Function Call Result	Try? Result	Notes
1	Call parseInt("123")	Returns 123	Optional(123)	String "123" converts successfully
2	Call parseInt("abc")	Throws error	nil	String "abc" cannot convert, error caught by try?
3	Use result from try?	N/A	Optional(123) or nil	Result is optional Int or nil if error

💡 Execution stops after try? returns optional value or nil depending on success or error

Variable Tracker

Variable	Start	After 1	After 2	Final
result	nil	Optional(123)	nil	Depends on input string

Key Moments - 2 Insights

Why does try? return nil instead of crashing when an error happens?

Because try? catches the error internally and converts it to nil, as shown in execution_table row 2.

What type is the result variable after using try??

It is an optional type wrapping the function's return type, shown as Optional(123) or nil in variable_tracker.

Visual Quiz - 3 Questions

Look at the execution_table, what does try? return when parseInt throws an error?

A The error is thrown up and crashes the program

B An optional wrapping the error

C nil

D A default value like 0

💡 Hint

See execution_table row 2 where try? result is nil when error occurs

At which step does try? return Optional(123)?

A Step 2

B Step 1

C Step 3

D Never

💡 Hint

Check execution_table row 1 where parseInt returns 123 and try? wraps it

If parseInt always succeeds, how does variable_tracker for result change?

A result becomes Optional with value every time

B result stays nil

C result becomes non-optional Int

D result becomes an error

💡 Hint

See variable_tracker showing result changes to Optional(123) after success

Concept Snapshot

try? calls a throwing function and returns an optional result.
If function succeeds, try? returns Optional(value).
If function throws error, try? returns nil.
Use try? to safely handle errors without do-catch.
Result type is always optional of function's return type.

Full Transcript

In Swift, try? is used to call a function that might throw an error. Instead of crashing or requiring a do-catch block, try? catches any error and returns nil. If the function succeeds, try? returns the value wrapped as an optional. For example, calling try? parseInt("123") returns Optional(123). Calling try? parseInt("abc") returns nil because the string cannot be converted. This lets you handle errors simply by checking if the result is nil or not. The variable holding the try? result is always an optional type. This visual trace shows each step: calling the function, catching errors, and returning optional values or nil. Remember, try? is a safe way to get optional results from throwing functions.