Swift string via string literal vs initializer - string

Question

In other languages such as Java, under the hood there is actually a difference between string obtained via string literal vs initializer. In Swift, are they equivalent under the hood?
e.g.
var string:String = ""
var string:String = String()
Refer to this SO post for info on differences between literal and object in Java.

Answer 1

The declarations are equivalent according to the Apple docs:
Initializing an Empty String
To create an empty String value as the starting point for building a longer string, either assign an empty string literal to a variable, or initialize a new String instance with initializer syntax:
var emptyString = "" // empty string literal
var anotherEmptyString = String() // initializer syntax
// these two strings are both empty, and are equivalent to each other
Reference: https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/StringsAndCharacters.html
If we look at the assembly, we will see that the two constructors use identical instructions.
string.swift:
let str = String()
let str2 = ""
Compiled assembly (swiftc -emit-assembly string.swift):
.section __TEXT,__text,regular,pure_instructions
.macosx_version_min 14, 3
.globl _main
.align 4, 0x90
_main:
.cfi_startproc
pushq %rbp
Ltmp0:
.cfi_def_cfa_offset 16
Ltmp1:
.cfi_offset %rbp, -16
movq %rsp, %rbp
Ltmp2:
.cfi_def_cfa_register %rbp
subq $16, %rsp
movq _globalinit_33_1BDF70FFC18749BAB495A73B459ED2F0_token4#GOTPCREL(%rip), %rax
movq _globalinit_33_1BDF70FFC18749BAB495A73B459ED2F0_func4#GOTPCREL(%rip), %rcx
xorl %edx, %edx
movl %edi, -4(%rbp)
movq %rax, %rdi
movq %rsi, -16(%rbp)
movq %rcx, %rsi
callq _swift_once
movq _globalinit_33_1BDF70FFC18749BAB495A73B459ED2F0_token5#GOTPCREL(%rip), %rdi
movq _globalinit_33_1BDF70FFC18749BAB495A73B459ED2F0_func5#GOTPCREL(%rip), %rax
xorl %r8d, %r8d
movl %r8d, %edx
movq __TZvOSs7Process5_argcVSs5Int32#GOTPCREL(%rip), %rcx
movl -4(%rbp), %r8d
movl %r8d, (%rcx)
movq %rax, %rsi
callq _swift_once
movq __TZvOSs7Process11_unsafeArgvGVSs20UnsafeMutablePointerGS0_VSs4Int8__#GOTPCREL(%rip), %rax
movq -16(%rbp), %rcx
movq %rcx, (%rax)
callq __TFSSCfMSSFT_SS
leaq L___unnamed_1(%rip), %rdi
xorl %r8d, %r8d
movl %r8d, %esi
movl $1, %r8d
movq %rax, __Tv6string3strSS(%rip)
movq %rdx, __Tv6string3strSS+8(%rip)
movq %rcx, __Tv6string3strSS+16(%rip)
movl %r8d, %edx
callq __TFSSCfMSSFT21_builtinStringLiteralBp8byteSizeBw7isASCIIBi1__SS
xorl %r8d, %r8d
movq %rax, __Tv6string4str2SS(%rip)
movq %rdx, __Tv6string4str2SS+8(%rip)
movq %rcx, __Tv6string4str2SS+16(%rip)
movl %r8d, %eax
addq $16, %rsp
popq %rbp
retq
.cfi_endproc
.globl __Tv6string3strSS
.zerofill __DATA,__common,__Tv6string3strSS,24,3
.globl __Tv6string4str2SS
.zerofill __DATA,__common,__Tv6string4str2SS,24,3
.section __TEXT,__cstring,cstring_literals
L___unnamed_1:
.space 1
.no_dead_strip __Tv6string3strSS
.no_dead_strip __Tv6string4str2SS
.linker_option "-lswiftCore"
.section __DATA,__objc_imageinfo,regular,no_dead_strip
L_OBJC_IMAGE_INFO:
.long 0
.long 512
.subsections_via_symbols
Notice that the declarations for str and str2 have identical instructions:
xorl %r8d, %r8d
movl %r8d, %esi
movl $1, %r8d
movq %rax, __Tv6string3strSS(%rip)
movq %rdx, __Tv6string3strSS+8(%rip)
movq %rcx, __Tv6string3strSS+16(%rip)
movl %r8d, %edx
# ...
xorl %r8d, %r8d
movq %rax, __Tv6string4str2SS(%rip)
movq %rdx, __Tv6string4str2SS+8(%rip)
movq %rcx, __Tv6string4str2SS+16(%rip)
movl %r8d, %eax
You can learn more about String literals by reviewing the Apple's documentation.