Diff btw var vs dynamic

Overview

Both

var

dynamic

var — Type Inferred at Compile Time

var

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var name = 'Alice';     // Inferred as String
var age = 28;           // Inferred as int
var price = 9.99;       // Inferred as double

// ❌ Cannot change type after inference
name = 'Bob';     // ✅ Still String — OK
// name = 42;     // ❌ Compile error — String expected

// var with no initial value → dynamic type
var x;            // Becomes dynamic
x = 42;
x = 'hello';     // ✅ No error (was dynamic)

dynamic — No Type Checking

dynamic

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dynamic anything = 42;
anything = 'now a string'; // ✅ No error
anything = true;            // ✅ No error
anything = [1, 2, 3];      // ✅ No error

// No compile-time checking
dynamic value = 'hello';
print(value.nonExistentMethod()); // ❌ Runtime error (not caught at compile!)

Key Differences

var

dynamic

When to Use Which

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// ✅ Use var for local variables where type is obvious
var users = <User>[];
var response = await http.get(url);

// ✅ Use dynamic only when you truly don't know the type
dynamic jsonValue = jsonDecode(response.body); // Could be Map or List
void serialize(dynamic obj) { ... } // Accepts unknown types

// ✅ Even better — use explicit types or generics over dynamic
Map<String, dynamic> json = jsonDecode(body); // Better — Map with dynamic values

Comparison with Other Keywords

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var name = 'Alice';       // Inferred = String, type-safe
dynamic name = 'Alice';   // No type checking
String name = 'Alice';    // Explicit — most clear
Object name = 'Alice';    // Any non-null Dart object
Object? name = null;      // Any object or null

Best Practice: Use

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var

for local variables (type is obvious from context). Avoid

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dynamic

— use proper types, generics, or

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Object?

when you need flexibility.

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dynamic

removes Dart's compile-time safety net.