# E4142

This 'const' declaration is not constant.

In MoonBit, you can use `const` to declare a constant value. Only literal value
of immutable primitive types can be assigned to `const`.

- These are constant values: `1`, `"String"`, `1.0`, `true`, `false`, etc.
- These are not constant values: `[1, 2, 3]`, `1 + 1`, `fn() { 1 }`, etc.

## Erroneous example

```{literalinclude} /sources/error_codes/4142_error/top.mbt
:language: moonbit
```

## Suggestion

As it is not possible to run the computation at compile time and assign the
result to a `const`, you can use a `let` declaration to calculate these result
at initialization time instead.

```{literalinclude} /sources/error_codes/4142_fixed/top.mbt
:language: moonbit
```

If you can compute the value yourself by using, say a calculator, you can
simply assign the result to the `const`.

```{literalinclude} /sources/error_codes/4142_fixed/top_1.mbt
:language: moonbit
```