Float Literals

Plain

Any valid integer constant shown in the previous section is also a valid float constant and can be passed to a value of a float type like f64.

Fractions

Unlike integers, floats may be fractions.

Exponents

Exponents to base ten can be added using E, to base two using P, followed by an optional sign + or - and the exponent values.

Overflows

Values that do not fit into the type they are assigned to will cause a compile time error:

Underflows

An underflow, i.e., a value that is so small that it would be rounded to zero, is considered an error:

Bases

Just like integer constants, float constants can be given in decimal, binary, octal or hexadecimal representation. A prefix 0d, 0b, 0o or 0x, respectively, selects the base to be used. If no prefix is given, decimal representation using base 10 is used as default. The base can be selected individually for the significand and for the exponent:

Types

The type of a float literal that is assigned to a field is inferred from that field. If the field, however, has itself a type that is inferred from the value assigned to it, the type of the float literal is f64. To distinguish floats from integers, a decimal point is required in this case, even if the float literal represents an integer.

When performing calculations with float literals using infix operators, the type of the calculation depends on the left operand:

To explicitly choose a type for a literal, you place the name of the type in front of it as in f32 1:

When adding the type explicitly before the float literal, you actually call the constructor of that type giving the constant as an argument. All built-in numeric types have a constructor with one argument val that has the same type. Consequently, the type inference mechanism forces that type onto the constant.