#Free pascal pointer record array code#
#Free pascal pointer record array free#

In my case, the A record was holding references to dynamic arrays, and it was those array elements that I was able to reassign through a constref parameter, which confused me: A = record

#Free pascal pointer record array code#

In other words, should I use constref whenever I do not reassign a formal parameter and I want to enforce passing a record by reference, or only when that record is also truly immutable in the sense that the procedure does not write to any of its fields either? But also, what is the difference from the perspective of the compiler, since apparently it does not catch the fact that even with constref I am able to mutate fields of a record that is passed by reference?Īs the responder points out, the above sample code should (and does) fail to compile with fpc 3.x I had oversimplified. I was able to compile this just fine under fpc 3.0.4 with either var or constref, but my gut feeling is that rec should probably be declared as var here so as to indicate that the memory occupied by this record instance is changed by the procedure call? type Rptr real Cptr char Bptr Boolean Aptr array1.5 of real date-ptr date Date record Day: 1.31 Month: 1.12 Year: 1900. proc does not reassign rec, but it does perform a side-effect in that it mutates fields of its formal parameter. This distinction makes sense for simple types such as numbers and strings, but what about structured types? Assuming I have the following record: A = recordĪnd a procedure that acts on As like the following: procedure proc(var rec: A)

var suggests mutation of the argument is possible, while const does not.

The base type could be anything like, integer, real, Boolean, enumerated. Where, the base-type indicates the type of the components of the file. A files type is determined by the type of the components.

Both var and constref enforce that a parameter is passed by reference Pascal treats a file as a sequence of components, which must be of uniform type.

This program creates an array, places the data into the array, then prints the data to the screen. The array can hold the record without violating its data type rules. The record can hold multiple data of different data types, but sill be of type record.

#Free pascal pointer record array free#

I've been reading about the various means of passing parameters to procedures and functions, but I am still confused about the semantics of var and constref as they apply to records (this is regarding the Free Pascal dialect of the language, v3.x). PlayerName: String PlayerScore: Integer End TScoreArray array 1.10 of TScores. The record type can get around the problem of arrays requiring the same data type.