This is a small follow up to my previous post about vars and consts.
In my post I was wonder why var input = "Hello Zig".* would let me edit it input[0] = 'a', for example, when string literals are constants.
As pointed out by @kristoff , turns out "Literal".* creates a copy on the stack.
This can be verified by looking at the generated assembly (x86_64 atleast)
0000000000225aa0 <main>:
225aa0: 55 push rbp
225aa1: 48 89 e5 mov rbp,rsp
225aa4: 48 83 ec 20 sub rsp,0x20
225aa8: 48 8b 04 25 e2 38 20 mov rax,QWORD PTR ds:0x2038e2
225aaf: 00
225ab0: 48 89 45 f6 mov QWORD PTR [rbp-0xa],rax
225ab4: 66 8b 04 25 ea 38 20 mov ax,WORD PTR ds:0x2038ea
225abb: 00
225abc: 66 89 45 fe mov WORD PTR [rbp-0x2],ax
225ac0: 48 8b 45 f6 mov rax,QWORD PTR [rbp-0xa]
225ac4: 48 89 45 e8 mov QWORD PTR [rbp-0x18],rax
225ac8: 66 8b 45 fe mov ax,WORD PTR [rbp-0x2]
225acc: 66 89 45 f0 mov WORD PTR [rbp-0x10],ax
225ad0: 48 8d 7d e8 lea rdi,[rbp-0x18]
225ad4: e8 e7 5c 00 00 call 22b7c0 <std.debug.print.103>
225ad9: 48 83 c4 20 add rsp,0x20
225add: 5d pop rbp
225ade: c3 ret
225adf: 90 nop
0x2038ea points to the address where our string is stored in the ELF
2038e0 29004861 69207468 65726500 64776172 ).Hai there.dwar
2038f0 663a2075 6e68616e 646c6564 20666f72 f: unhandled for
We first make 32 bytes of space on the stack (sub rsp 0x20) and then copy the string literal starting at address 0xa to 0x2 using 2 instructions ("Hai There" is 9 bytes, so we copy 8 bytes using the first instruction and then the last byte using another)
We then copy the string into the stack from rbp-0x18 to rbp-0x10 and call debug.print with the base address to our copy (rbp-0x18)
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