Difference between revisions of "EDT:EGL Language Primitive Types"

Revision as of 09:58, 21 July 2011

Please see the parent of this page, EDT:EGL Language.

Primitive Types (Table 3)

Notes on Table 3

1. Date and timestamp are the only supported date/time types. Use a timestamp in place of RBD's time, and use a numeric type in place of RBD's interval.
2. Decimal with no length or decimals is a reference type with an immutable value.
3. Number is a reference type with an immutable value. Unlike in RBD, number variables can be declared anywhere a variable declaration is allowed.
4. Bytes(N) is a value type similar to RBD's hex. N indicates the number of bytes in the value. (In RBD, the length of a hex is the number of nibbles not the nubmer of bytes.)
5. Bytes with no length is a reference type with an immutable value of any length.
   
6. Timestamp with no pattern is a reference type in EDT.  It can hold any timestamp value.
7. As in RBD, it's OK to only specify the length when using the decimal type. Decimal(N) is internally mapped to decimal(N,0).
8. Value types may be nullable.
9. Value typed variables may be declared with a question mark following the name of the type to indicate that they're nullable. Nullability means that a variable may really be null. It's not an "I'm null" flag like in RBD. A NullValueException will be thrown if you try to access a field or function of a null variable, even a record. A NullValueException will be thrown if a null variable is an operand to a math operator, an array access, a substring access, a comparison, or a bitwise operator. The string concatenation operators will work the same as in RBD with respect to nulls. :: treats null as the empty string, and ?: results in null if either operand is null. A question mark won't be allowed on the second operand of the AS and ISA operators (the name of the type).
   

More about the Bytes type

Bytes is meant to hold data with no particular format.

Assignment between two bytes values with no length is a reference assignment. Assignment between two bytes values when one or both has a length is a value assignment (data is copied). If the source is longer bytes on its right side are truncated. If the source is shorter then we don't add padding: we just don't update what was there before. For example if your bytes(3) is 0x123456 and you assign it a bytes(1) value of 0x99 then the bytes(3) ends up with 0x993456.

In order for two bytes values to be compared, they must both have a size, and the sizes must be equal. The comparison is done one byte at a time, from left to right, until a difference is found. The operand with a one instead of a zero is greater.

The bytes type supports the substring operator. The type of the result is bytes (with no length).