Enums in Blockchain / Solidity - Step-by-Step Execution

Concept Flow - Enums

Define Enum with named values

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Use Enum value in code

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Compare or switch on Enum

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Execute code based on Enum case

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End

Enums let you create named constants to represent fixed options, making code clearer and safer.

Execution Sample

Blockchain / Solidity

enum Status {
  Pending,
  Confirmed,
  Failed
}

let txStatus = Status.Pending;

Defines a transaction status enum and sets a variable to the Pending status.

Execution Table

Step	Action	Enum State	Variable txStatus	Notes
1	Define enum Status with values Pending=0, Confirmed=1, Failed=2	Status = {Pending:0, Confirmed:1, Failed:2}	undefined	Enum created with named values
2	Assign txStatus = Status.Pending	Status unchanged	0	txStatus holds enum value 0 (Pending)
3	Check if txStatus == Status.Pending	Status unchanged	0	Condition true, code for Pending runs
4	Update txStatus = Status.Confirmed	Status unchanged	1	txStatus updated to Confirmed
5	Check if txStatus == Status.Failed	Status unchanged	1	Condition false, code for Failed skipped
6	End of example	Status unchanged	1	Execution stops

💡 Reached end of code after enum usage and checks

Variable Tracker

Variable	Start	After Step 2	After Step 4	Final
txStatus	undefined	0 (Pending)	1 (Confirmed)	1 (Confirmed)

Key Moments - 2 Insights

Why does txStatus hold a number instead of the word 'Pending'?

Enums assign numbers to names internally (Pending=0). txStatus stores the number for efficiency, but code uses the name for clarity (see execution_table step 2).

What happens if we compare txStatus to a wrong enum value?

The comparison fails because txStatus holds a specific number. For example, at step 5, txStatus=1 (Confirmed) is not equal to Failed=2, so that branch is skipped.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of txStatus after step 2?

A 2 (Failed)

B 1 (Confirmed)

C 0 (Pending)

D undefined

💡 Hint

Check the 'Variable txStatus' column at step 2 in the execution_table.

At which step does txStatus change from Pending to Confirmed?

A Step 3

B Step 4

C Step 5

D Step 6

💡 Hint

Look at the 'Variable txStatus' column changes between steps in the execution_table.

If txStatus was set to Status.Failed at step 2, what would happen at step 3?

A The condition txStatus == Status.Pending would be false

B The condition txStatus == Status.Pending would be true

C txStatus would automatically change to Pending

D The program would crash

💡 Hint

Refer to how comparisons work in the execution_table and variable_tracker.

Concept Snapshot

Enums create named constants with fixed values.
Use enum names in code for clarity.
Internally, enums store numbers.
Compare enum variables to enum names.
Helps avoid magic numbers and bugs.

Full Transcript

Enums let you define a set of named values representing fixed options, like transaction statuses. In the example, we define an enum Status with Pending, Confirmed, and Failed. Each name maps to a number starting at 0. We assign txStatus to Status.Pending, which is 0 internally. Then we check txStatus against enum values to decide what code to run. Changing txStatus to Confirmed updates its value to 1. Comparing txStatus to a different enum value returns false if they don't match. This makes code easier to read and less error-prone than using raw numbers.