BuildBlock for combining results in Swift - Step-by-Step Execution

Concept Flow - BuildBlock for combining results

Start BuildBlock

↓

Evaluate each Result

↓

Check if all are success?

No→Return first failure

Yes↓

Combine success values

↓

Return combined success

The BuildBlock evaluates multiple Result values, returns the first failure if any, otherwise combines all successes.

Execution Sample

Swift

func combineResults() -> Result<(Int, Int, Int), String> {
    Result.buildBlock(
        .success(10),
        .success(20),
        .failure("Error")
    )
}

This code combines three Result values, returning the first failure or combined successes.

Execution Table

Step	Action	Result Evaluated	Outcome	Return Value
1	Evaluate first Result	success(10)	Success	Continue
2	Evaluate second Result	success(20)	Success	Continue
3	Evaluate third Result	failure("Error")	Failure found	Return failure("Error")
4	Stop evaluation	N/A	Failure returned	failure("Error")

💡 Third Result is failure, so BuildBlock returns failure immediately.

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
results	N/A	success(10)	[success(10), success(20)]	[success(10), success(20), failure("Error")]	failure("Error")

Key Moments - 2 Insights

Why does BuildBlock return failure immediately instead of combining all results?

Because BuildBlock stops at the first failure it finds, as shown in execution_table row 3, it returns failure("Error") without combining successes.

What happens if all Results are successes?

BuildBlock combines all success values into a tuple or combined value, as described in concept_flow and would return combined success.

Visual Quiz - 3 Questions

Look at the execution_table, what is the return value at step 3?

A success(20)

B failure("Error")

C success(10)

D combined successes

💡 Hint

Check execution_table row 3 where failure is found and returned.

At which step does BuildBlock stop evaluating further Results?

A Step 3

B Step 2

C Step 1

D Step 4

💡 Hint

See execution_table row 3 where failure is detected and evaluation stops.

If all Results were successes, what would BuildBlock return?

A The first success only

B A failure

C A combined success of all values

D An empty result

💡 Hint

Refer to concept_flow and key_moments about combining all successes.

Concept Snapshot

BuildBlock combines multiple Result values.
It returns the first failure found.
If all succeed, it combines success values.
Useful for aggregating multiple operations.
Stops early on failure to save work.

Full Transcript

This visual execution shows how Swift's BuildBlock combines multiple Result values. It evaluates each Result in order. If it finds a failure, it returns that failure immediately without checking others. If all are successes, it combines their values into one success. The execution table traces each step, showing evaluation and return values. The variable tracker shows how the list of results grows and ends with the failure. Key moments clarify why BuildBlock stops early and what happens if all succeed. The quiz tests understanding of these steps and outcomes.

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