Reference types behavior in Blockchain / Solidity - Step-by-Step Execution

Concept Flow - Reference types behavior

Create Object A

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Assign Ref1 = A

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Assign Ref2 = Ref1

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Modify via Ref2

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Check Ref1 shows change

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Reassign Ref2 to new Object B

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Ref1 still points to A

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End

This flow shows how reference types point to the same object, so changes via one reference affect the other, but reassigning a reference breaks the link.

Execution Sample

Blockchain / Solidity

objectA = {"value": 10}
ref1 = objectA
ref2 = ref1
ref2["value"] = 20
ref2 = {"value": 30}
print(ref1["value"])

This code shows two references to the same object, modifying it through one reference, then reassigning the second reference.

Execution Table

Step	Action	ref1	ref2	objectA	Output
1	Create objectA with value 10	null	null	{"value":10}
2	Assign ref1 = objectA	{"value":10}	null	{"value":10}
3	Assign ref2 = ref1	{"value":10}	{"value":10}	{"value":10}
4	Modify ref2["value"] = 20	{"value":20}	{"value":20}	{"value":20}
5	Reassign ref2 = {"value":30}	{"value":20}	{"value":30}	{"value":20}
6	Print ref1["value"]	{"value":20}	{"value":30}	{"value":20}	20

💡 Execution ends after printing ref1["value"] which is 20, showing ref1 still points to original object.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	After Step 5	Final
objectA	null	{"value":10}	{"value":10}	{"value":20}	{"value":20}	{"value":20}
ref1	null	{"value":10}	{"value":10}	{"value":20}	{"value":20}	{"value":20}
ref2	null	null	{"value":10}	{"value":20}	{"value":30}	{"value":30}

Key Moments - 2 Insights

Why does changing ref2["value"] also change ref1["value"]?

Because ref1 and ref2 both point to the same object (objectA) at that time, so modifying via one reference affects the shared object, as shown in step 4 of the execution_table.

Why does ref1["value"] stay 20 after ref2 is reassigned?

Reassigning ref2 to a new object breaks its link to objectA, but ref1 still points to the original objectA, so ref1["value"] remains 20, as seen in step 5 and 6.

Visual Quiz - 3 Questions

Look at the execution_table at step 4, what is the value of ref1["value"]?

A 10

B 20

C 30

D null

💡 Hint

Check the 'ref1' column at step 4 in the execution_table.

At which step does ref2 stop pointing to the same object as ref1?

A Step 5

B Step 3

C Step 4

D Step 6

💡 Hint

Look at when ref2 value changes independently in the execution_table.

If we changed ref2["value"] = 50 at step 4 instead of 20, what would ref1["value"] be at step 6?

A 20

B 30

C 50

D 10

💡 Hint

Since ref1 and ref2 share the same object before step 5, changes via ref2 affect ref1.

Concept Snapshot

Reference types store addresses to objects.
Multiple references can point to the same object.
Changing the object via one reference affects all references.
Reassigning a reference breaks the link to the original object.
Useful to understand shared state in blockchain data structures.

Full Transcript

This lesson shows how reference types behave in blockchain programming. We start by creating an object with a value. Then we assign two references to this same object. When we change the value through one reference, the other reference sees the change because they point to the same object. Later, when we assign a new object to one reference, it no longer points to the original object, but the other reference still does. This explains why changes through one reference affect others until reassignment breaks the link. Understanding this helps avoid bugs when working with shared data in blockchain code.