BuildBlock for combining results in Swift

Introduction

BuildBlock helps you combine multiple pieces of work that can succeed or fail into one result. It makes it easy to handle many results together.

When you want to run several tasks and collect all their success or failure results.

When you need to combine multiple validation checks into one overall result.

When you want to merge several small results into a bigger result in a clear way.

Syntax

Swift

func buildBlock(_ components: Result<Void, Error>...) -> Result<Void, Error> {
    for component in components {
        if case .failure(let error) = component {
            return .failure(error)
        }
    }
    return .success(())
}

This example shows a buildBlock function that combines multiple Result values.

If any component is a failure, it returns that failure immediately.

Examples

This combines two results. Since one is failure, combined is failure.

Swift

enum MyError: Error {
    case example
}

let result1: Result<Void, Error> = .success(())
let result2: Result<Void, Error> = .failure(MyError.example)

let combined = buildBlock(result1, result2)

Both results are success, so combined is success.

Swift

let result1: Result<Void, Error> = .success(())
let result2: Result<Void, Error> = .success(())

let combined = buildBlock(result1, result2)

Sample Program

This program defines a buildBlock function to combine multiple Result values. It prints whether the combined results are success or failure.

Swift

import Foundation

enum MyError: Error {
    case example
}

func buildBlock(_ components: Result<Void, Error>...) -> Result<Void, Error> {
    for component in components {
        if case .failure(let error) = component {
            return .failure(error)
        }
    }
    return .success(())
}

let successResult: Result<Void, Error> = .success(())
let failureResult: Result<Void, Error> = .failure(MyError.example)

let combined1 = buildBlock(successResult, successResult)
let combined2 = buildBlock(successResult, failureResult)

switch combined1 {
case .success:
    print("combined1: Success")
case .failure:
    print("combined1: Failure")
}

switch combined2 {
case .success:
    print("combined2: Success")
case .failure:
    print("combined2: Failure")
}

Important Notes

BuildBlock is useful in SwiftUI and result builders to combine multiple parts.

Here, it stops at the first failure to avoid unnecessary work.

Summary

BuildBlock combines multiple Result values into one.

It returns failure if any component fails, otherwise success.

This helps manage multiple results cleanly and clearly.

Practice

1. What does BuildBlock do when combining multiple Result values in Swift?

easy

A. It returns failure only if all Result values are failures.

B. It returns failure if any Result is failure, otherwise success.

C. It always returns success regardless of individual results.

D. It merges all success values into an array without checking failures.

Solution

1. Step 1: Understand BuildBlock behavior

   BuildBlock combines multiple Result values and checks each one.

2. Step 2: Check failure condition

   If any Result is a failure, the combined result is failure; otherwise, it is success.

3. Final Answer:

   It returns failure if any Result is failure, otherwise success. -> Option B

4. Quick Check:

   Failure if any fail = C [OK]

Hint: Remember: one failure causes whole BuildBlock to fail [OK]

Common Mistakes:

• Assuming it returns success if any result is success
• Thinking it merges all successes without failure check
• Believing it fails only if all results fail

2. Which of the following is the correct syntax to combine two Result values using BuildBlock in Swift?

easy

A. BuildBlock(result1, result2)

B. BuildBlock[result1, result2]

C. BuildBlock{result1, result2}

D. BuildBlock->(result1, result2)

Solution

1. Step 1: Recall BuildBlock usage

   BuildBlock is called like a function with comma-separated arguments inside parentheses.

2. Step 2: Identify correct syntax

   Only BuildBlock(result1, result2) matches the correct function call syntax.

3. Final Answer:

   BuildBlock(result1, result2) -> Option A

4. Quick Check:

   Function call syntax = A [OK]

Hint: Use parentheses for function calls, not brackets or braces [OK]

Common Mistakes:

• Using square brackets instead of parentheses
• Using braces which are for closures
• Using arrow syntax which is invalid here

3. What is the output of this Swift code?

let r1: Result = .success(10)
let r2: Result = .failure(NSError(domain: "", code: 1))
let combined = BuildBlock(r1, r2)
switch combined {
 case .success(let values): print(values)
 case .failure(let error): print("Error code: \((error as NSError).code)")
}

medium

A. Error code: 1

B. 10

C. Error code: 0

D. Compilation error

Solution

1. Step 1: Analyze input results

   r1 is success with 10, r2 is failure with error code 1.

2. Step 2: Understand BuildBlock combining

   Since r2 is failure, combined result is failure with that error.

3. Step 3: Switch prints error code

   The failure case prints "Error code: 1" from the NSError code.

4. Final Answer:

   Error code: 1 -> Option A

5. Quick Check:

   Failure present, print error code 1 = A [OK]

Hint: If any result fails, output error info, not success value [OK]

Common Mistakes:

• Assuming success prints 10 despite failure
• Confusing error code with 0
• Expecting compilation error due to BuildBlock

4. Identify the error in this Swift code using BuildBlock:

let r1: Result = .success("Hi")
let r2: Result = .success("There")
let combined = BuildBlock(r1 + r2)

medium

A. BuildBlock cannot combine success values.

B. BuildBlock requires at least three arguments.

C. Result types must be integers to combine.

D. You cannot use + operator directly on Result types.

Solution

1. Step 1: Check operator usage on Result

   The code tries to add two Result values with +, which is invalid.

2. Step 2: Understand correct BuildBlock usage

   BuildBlock takes multiple Result arguments separately, not combined with +.

3. Final Answer:

   You cannot use + operator directly on Result types. -> Option D

4. Quick Check:

   + operator invalid on Result = D [OK]

Hint: Pass results as separate arguments, not combined with + [OK]

Common Mistakes:

• Trying to add Result values directly
• Thinking BuildBlock needs 3+ arguments
• Believing only integers can be combined

5. You have three Result values:

let r1: Result = .success(5)
let r2: Result = .success(10)
let r3: Result = .success(15)

Using BuildBlock, how can you combine them to get a single Result with an array of all success values?

hard

A. Use BuildBlock(r1, r2, r3) directly; it returns array of values.

B. Use BuildBlock(r1, r2, r3).flatMap { [$0 + $1 + $2] }

C. Use BuildBlock(r1, r2, r3).map { [$0, $1, $2] }

D. Use BuildBlock([r1, r2, r3]) to combine into array.

Solution

1. Step 1: Understand BuildBlock output

   It combines multiple Result values into a single Result with a tuple of success values.

2. Step 2: Convert tuple to array

   Use map to transform the tuple ($0, $1, $2) into an array [$0, $1, $2].

3. Final Answer:

   Use BuildBlock(r1, r2, r3).map { [$0, $1, $2] } -> Option C

4. Quick Check:

   Map tuple to array after BuildBlock = B [OK]

Hint: BuildBlock returns tuple; map it to array for combined values [OK]

Common Mistakes:

• Expecting BuildBlock to return array directly
• Using flatMap incorrectly to sum values
• Passing array of results instead of separate arguments