4.1 Fortran 2003 status

GNU Fortran supports several Fortran 2003 features; an incomplete list can be found below. See also the wiki page about Fortran 2003.

• Procedure pointers including procedure-pointer components with PASS attribute.
• Procedures which are bound to a derived type (type-bound procedures) including PASS, PROCEDURE and GENERIC, and operators bound to a type.
• Abstract interfaces and type extension with the possibility to override type-bound procedures or to have deferred binding.
• Polymorphic entities (“CLASS”) for derived types and unlimited polymorphism (“CLASS(*)”) – including SAME_TYPE_AS, EXTENDS_TYPE_OF and SELECT TYPE for scalars and arrays and finalization.
• Generic interface names, which have the same name as derived types, are now supported. This allows one to write constructor functions. Note that Fortran does not support static constructor functions. For static variables, only default initialization or structure-constructor initialization are available.
• The ASSOCIATE construct.
• Interoperability with C including enumerations,
• In structure constructors the components with default values may be omitted.
• Extensions to the ALLOCATE statement, allowing for a type-specification with type parameter and for allocation and initialization from a SOURCE= expression; ALLOCATE and DEALLOCATE optionally return an error message string via ERRMSG=.
• Reallocation on assignment: If an intrinsic assignment is used, an allocatable variable on the left-hand side is automatically allocated (if unallocated) or reallocated (if the shape is different). Currently, scalar deferred character length left-hand sides are correctly handled but arrays are not yet fully implemented.
• Deferred-length character variables and scalar deferred-length character components of derived types are supported. (Note that array-valued compoents are not yet implemented.)
• Transferring of allocations via MOVE_ALLOC.
• The PRIVATE and PUBLIC attributes may be given individually to derived-type components.
• In pointer assignments, the lower bound may be specified and the remapping of elements is supported.
• For pointers an INTENT may be specified which affect the association status not the value of the pointer target.
• Intrinsics command_argument_count, get_command, get_command_argument, and get_environment_variable.
• Support for Unicode characters (ISO 10646) and UTF-8, including the SELECTED_CHAR_KIND and NEW_LINE intrinsic functions.
• Support for binary, octal and hexadecimal (BOZ) constants in the intrinsic functions INT, REAL, CMPLX and DBLE.
• Support for namelist variables with allocatable and pointer attribute and nonconstant length type parameter.
• Array constructors using square brackets. That is, [...] rather than (/.../). Type-specification for array constructors like (/ some-type :: ... /).
• Extensions to the specification and initialization expressions, including the support for intrinsics with real and complex arguments.
• Support for the asynchronous input/output syntax; however, the data transfer is currently always synchronously performed.
• FLUSH statement.
• IOMSG= specifier for I/O statements.
• Support for the declaration of enumeration constants via the ENUM and ENUMERATOR statements. Interoperability with gcc is guaranteed also for the case where the -fshort-enums command line option is given.
• TR 15581:
  • ALLOCATABLE dummy arguments.
  • ALLOCATABLE function results
  • ALLOCATABLE components of derived types
• The OPEN statement supports the ACCESS='STREAM' specifier, allowing I/O without any record structure.
• Namelist input/output for internal files.
• Minor I/O features: Rounding during formatted output, using of a decimal comma instead of a decimal point, setting whether a plus sign should appear for positive numbers. On systems where strtod honours the rounding mode, the rounding mode is also supported for input.
• The PROTECTED statement and attribute.
• The VALUE statement and attribute.
• The VOLATILE statement and attribute.
• The IMPORT statement, allowing to import host-associated derived types.
• The intrinsic modules ISO_FORTRAN_ENVIRONMENT is supported, which contains parameters of the I/O units, storage sizes. Additionally, procedures for C interoperability are available in the ISO_C_BINDING module.
• USE statement with INTRINSIC and NON_INTRINSIC attribute; supported intrinsic modules: ISO_FORTRAN_ENV, ISO_C_BINDING, OMP_LIB and OMP_LIB_KINDS, and OPENACC.
• Renaming of operators in the USE statement.

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