Macro validated_constructor 

macro_rules! validated_constructor {
    ($name:ident, $field:ident: f32, probability) => { ... };
    ($name:ident, $field:ident: ($t1:ty, $t2:ty), range) => { ... };
    ($name:ident, $field:ident: $t:ty, positive) => { ... };
    ($name:ident, size: ($t1:ty, $t2:ty)) => { ... };
    ($name:ident, $($field:ident: $t:ty),+, validate = $validator:expr) => { ... };
}

Macro to create a simple constructor with validation