Parallel Computer Centre
The redundant features of Fortran 90 fall into five groups: Source form, Data, Control, Procedures and Input/Output.
The use of modules is recommended rather than the INCLUDE line. The INCLUDE line contained a character literal constant indicating what text should be inserted at a specified point or where text to be inserted should be obtained from.
The dangerous concept of implicit typing and the IMPLICIT statement should not be used. The IMPLICIT NONE statement should be included at the beginning of every program unit to ensure explicit declaration of all variables.
The new form of declaring variables with a double colon (::) between the type and the list of variables is recommended. Additionally, the use of attribute forms of PARAMETER, DIMENSION, etc., in the type declaration, rather than the statement forms is recommended.
The DATA statement is no longer generally needed as variables may now be initialised in a type statement. Exceptions to this are octal, hexadecimal and array section initialisations.
The only form of adjustable size array in Fortran 77 was the assumed-size array. In Fortran 90 this has been superseded by the assumed-shape array, and thus the assumed-size array should no longer be used in new programs.
COMMON blocks and BLOCK DATA should no longer be used as the use of modules obviates the need for them. Similarly the EQUIVALENCE statement has become unnecessary due to the introduction of modules, dynamic storage allocation, pointers, and the intrinsic function TRANSFER.
It is recommended that the SEQUENCE attribute is never used.
With the introduction of modern control constructs and the character string format specifications, the need for labels is redundant.
The DO construct and EXIT and CYCLE statements replace the use of the CONTINUE statement to end a DO loop.
GO TO and computed GO TO statements should be avoided, using IF, DO and CASE constructs, and EXIT and CYCLE statements instead.
The DO WHILE statement was introduced in Fortran 90. This functionality can equally be provided using the DO loop construct and EXIT statement, and this form is recommended.
The ENTRY statement allows a procedure to have more than one entry point. The introduction of modules, where each entry point becomes a module procedure, has made the ENTRY statement unnecessary.
The statement function provided a means of defining and using a one-line function. This has been superseded by the concept of internal procedures.
The use of module procedures and internal procedures means that it is not necessary to use external procedures. Thus, external procedures and the EXTERNAL statement are effectively redundant.
The END, EOR and ERR specifiers are used when exceptional conditions occur in input and output. It is recommended that the IOSTAT specifier is used instead of these.
Namelist input/output is a poorly designed feature and it is recommended that namelist should not be used unless absolutely necessary.
Finally, it is recommended that six edit descriptors should not be used, namely, D, BN, BZ, P, G and X.
The D edit descriptor has been superseded by the E edit descriptor, and the BN and BZ edit descriptors have both been replaced by the BLANK specifier.
The P edit descriptor allows numeric data to be scaled on either input or output, however this can lead to unnecessary confusion and is therefore best avoided.
The G edit descriptor is a generalized edit descriptor which can be used to input or output values of any intrinsic type. However, the use of I, E, EN, F, L or A edit descriptors is preferable as these provide some check that the data types are correct.
The X edit descriptor has the same effect as the TR edit descriptor, and the latter is recommended.