官方的 ivar_getTypeEncoding/ property_getAttributes(property) 返回说明
c
A char
I
An int
s
A short
l
A long
l is treated as a 32-bit quantity on 64-bit programs.
q
A long long
C
An unsigned char
I
An unsigned int
S
An unsigned short
L
An unsigned long
Q
An unsigned long long
f
A float
d
A double
B
A C++ bool or a C99 _Bool
v
A void
\*
A character string (char *)
@
An object (whether statically typed or typed id)
#
A class object (Class)
:
A method selector (SEL)
[array type]
An array
{name=type...}
A structure
(name=type...)
A union
bnum
A bit field of num bits
^type
A pointer to type
?
An unknown type (among other things, this code is used for function pointers)
