---
title: Variables
description: Local state management with type inference and explicit mutability.
icon: Variable
---

In Mist, variables follow the language-wide `type name` convention. For local scope, the `var` keyword provides type inference, while explicit types can be used for clarity or strictness.

## Basic Declaration

Variables are declared using the `var` keyword for automatic type inference. Like Rust, variables are immutable by default.

```java
var message = "Hello Mist"; // Inferred as str*
var count = 42;             // Inferred as i32
```

## Mutability

To allow a variable to be reassigned, use the `mut` modifier after the `var` keyword or the explicit type.

```rust
var mut score = 0;
score = 100;

f32 mut price = 19.99;
price = 14.99;
```

## Explicit Typing

While `var` handles inference, you can explicitly define the type before the identifier. This is often used for clarity in complex logic or when the specific numeric width (e.g., `u8` vs `i32`) matters.

```rust
u64 large_id = 1000234;
bool is_active = true;
```

## Constants

Constants are immutable values that are evaluated at compile time. They require an explicit type and follow the `const` keyword.

```rust
const i32 MAX_RETRIES = 5;
const str* VERSION = "1.0.4";
```

## Key Characteristics

- **Predictable Order**: Whether using `var` or an explicit type, the name of the variable always follows the "source" of its data.
- **Safety First**: Immutability by default prevents accidental state changes, mapping directly to Rust's memory safety model.
- **Zero-Cost Inference**: Type inference is handled entirely at compile time, ensuring there is no runtime performance penalty.
- **Shadowing**: Mist supports variable shadowing, allowing you to reuse variable names within the same scope to transform data without changing mutability.