diff --git a/compiler/msvc_win.v b/compiler/msvc_win.v
index 1e00938355..9452e3dca3 100644
--- a/compiler/msvc_win.v
+++ b/compiler/msvc_win.v
@@ -196,7 +196,7 @@ fn find_msvc() ?MsvcResult {
 	}
 }
 
-pub fn cc_msvc(v *V) {
+pub fn cc_msvc(v mut V) {
 	r := find_msvc() or {
 		println('Could not find MSVC')
 		
diff --git a/vlib/bf/bf.v b/vlib/bf/bf.v
index 2d829d3ce1..03f9701be3 100644
--- a/vlib/bf/bf.v
+++ b/vlib/bf/bf.v
@@ -37,15 +37,15 @@ fn bitget(instance BitField, bitnr int) int {
 	return (instance.field[bitslot(bitnr)] >> u32(bitnr % SLOT_SIZE)) & 1
 }
 
-fn bitset(instance BitField, bitnr int) {
+fn bitset(instance mut BitField, bitnr int) {
 	instance.field[bitslot(bitnr)] = instance.field[bitslot(bitnr)] | bitmask(bitnr)
 }
 
-fn bitclear(instance BitField, bitnr int) {
+fn bitclear(instance mut BitField, bitnr int) {
 	instance.field[bitslot(bitnr)] = instance.field[bitslot(bitnr)] & ~bitmask(bitnr)
 }
 
-fn bittoggle(instance BitField, bitnr int) {
+fn bittoggle(instance mut BitField, bitnr int) {
 	instance.field[bitslot(bitnr)] = instance.field[bitslot(bitnr)] ^ bitmask(bitnr)
 }
 /*
@@ -65,7 +65,7 @@ fn bitnslots(length int) int {
 	return (length - 1) / SLOT_SIZE + 1
 } 
 
-fn cleartail(instance BitField) {
+fn cleartail(instance mut BitField) {
 	tail := instance.size % SLOT_SIZE
 	if tail != 0 {
 		// create a mask for the tail 
diff --git a/vlib/crypto/aes/aes_cbc.v b/vlib/crypto/aes/aes_cbc.v
index abca512bc2..968025b026 100644
--- a/vlib/crypto/aes/aes_cbc.v
+++ b/vlib/crypto/aes/aes_cbc.v
@@ -62,7 +62,7 @@ pub fn (x &AesCbc) encrypt_blocks(dst, src []byte) {
 
 	for src.len > 0 {
 		// Write the xor to dst, then encrypt in place.
-		cipher.xor_bytes(dst.left(x.block_size), src.left(x.block_size), iv)
+		cipher.xor_bytes(mut dst.left(x.block_size), src.left(x.block_size), iv)
 		x.b.encrypt(dst.left(x.block_size), dst.left(x.block_size))
 
 		// Move to the next block with this block as the next iv.
@@ -79,7 +79,7 @@ pub fn (x &AesCbc) encrypt_blocks(dst, src []byte) {
 	copy(x.iv, iv)
 }
 
-pub fn (x &AesCbc) decrypt_blocks(dst, src []byte) {
+pub fn (x &AesCbc) decrypt_blocks(dst mut []byte, src []byte) {
 	if src.len%x.block_size != 0 {
 		panic('crypto.cipher: input not full blocks')
 	}
@@ -114,7 +114,7 @@ pub fn (x &AesCbc) decrypt_blocks(dst, src []byte) {
 
 	// The first block is special because it uses the saved iv.
 	x.b.decrypt(dst.slice(start, end), src.slice(start, end))
-	cipher.xor_bytes(dst.slice(start, end), dst.slice(start, end), x.iv)
+	cipher.xor_bytes(mut dst.slice(start, end), dst.slice(start, end), x.iv)
 
 
 	// Set the new iv to the first block we copied earlier.
diff --git a/vlib/crypto/aes/block_generic.v b/vlib/crypto/aes/block_generic.v
index 439d8dbd67..a799187666 100644
--- a/vlib/crypto/aes/block_generic.v
+++ b/vlib/crypto/aes/block_generic.v
@@ -87,10 +87,10 @@ fn encrypt_block_generic(xk []u32, dst, src []byte) {
 	s3 ^= xk[k+3]
 
 	_ = dst[15] // early bounds check
-	binary.big_endian_put_u32(dst.left(4), s0)
-	binary.big_endian_put_u32(dst.slice(4, 8), s1)
-	binary.big_endian_put_u32(dst.slice(8, 12), s2)
-	binary.big_endian_put_u32(dst.slice(12, 16), s3)
+	binary.big_endian_put_u32(mut dst.left(4), s0)
+	binary.big_endian_put_u32(mut dst.slice(4, 8), s1)
+	binary.big_endian_put_u32(mut dst.slice(8, 12), s2)
+	binary.big_endian_put_u32(mut dst.slice(12, 16), s3)
 }
 
 // Decrypt one block from src into dst, using the expanded key xk.
@@ -141,10 +141,10 @@ fn decrypt_block_generic(xk []u32, dst, src []byte) {
 	s3 ^= xk[k+3]
 
 	_ = dst[15] // early bounds check
-	binary.big_endian_put_u32(dst.left(4), s0)
-	binary.big_endian_put_u32(dst.slice(4, 8), s1)
-	binary.big_endian_put_u32(dst.slice(8, 12), s2)
-	binary.big_endian_put_u32(dst.slice(12, 16), s3)
+	binary.big_endian_put_u32(mut dst.left(4), s0)
+	binary.big_endian_put_u32(mut dst.slice(4, 8), s1)
+	binary.big_endian_put_u32(mut dst.slice(8, 12), s2)
+	binary.big_endian_put_u32(mut dst.slice(12, 16), s3)
 }
 
 // Apply SBox0 to each byte in w.
diff --git a/vlib/crypto/md5/md5.v b/vlib/crypto/md5/md5.v
index 62c541924e..5d22b52a44 100644
--- a/vlib/crypto/md5/md5.v
+++ b/vlib/crypto/md5/md5.v
@@ -127,14 +127,14 @@ pub fn (d mut Digest) checksum() []byte {
 // sum returns the MD5 checksum of the data.
 pub fn sum(data []byte) []byte {
 	mut d := new()
-	d.write(data)
+	d.write(mut data)
 	return d.checksum()
 }
 
-fn block(dig &Digest, p []byte) {
+fn block(dig mut Digest, p []byte) {
     // For now just use block_generic until we have specific
 	// architecture optimized versions
-    block_generic(dig, p)
+    block_generic(mut dig, p)
 }
 
 pub fn (d &Digest) size() int { return Size }
diff --git a/vlib/crypto/rc4/rc4.v b/vlib/crypto/rc4/rc4.v
index 6f0e45b1b0..0117a13c30 100644
--- a/vlib/crypto/rc4/rc4.v
+++ b/vlib/crypto/rc4/rc4.v
@@ -49,7 +49,7 @@ pub fn new_cipher(key []byte) ?Cipher {
 //
 // Deprecated: Reset can't guarantee that the key will be entirely removed from
 // the process's memory.
-pub fn (c &Cipher) reset() {
+pub fn (c mut Cipher) reset() {
 	for i in c.s {
 		c.s[i] = u32(0)
 	}
@@ -59,7 +59,7 @@ pub fn (c &Cipher) reset() {
 
 // xor_key_stream sets dst to the result of XORing src with the key stream.
 // Dst and src must overlap entirely or not at all.
-pub fn (c &Cipher) xor_key_stream(dst, src []byte) {
+pub fn (c mut Cipher) xor_key_stream(dst mut []byte, src []byte) {
 	if src.len == 0 {
 		return
 	}
diff --git a/vlib/crypto/rc4/rc4_test.v b/vlib/crypto/rc4/rc4_test.v
index 820bd0d584..1f90a22be7 100644
--- a/vlib/crypto/rc4/rc4_test.v
+++ b/vlib/crypto/rc4/rc4_test.v
@@ -15,7 +15,7 @@ fn test_crypto_rc4() {
 	mut src := 'toencrypt'.bytes()
 	
 	// src & dst same, encrypt in place
-	c.xor_key_stream(src, src) // encrypt data
+	c.xor_key_stream(mut src, src) // encrypt data
 	
 	c.reset()
 
diff --git a/vlib/crypto/sha1/sha1.v b/vlib/crypto/sha1/sha1.v
index 131224f34a..2d369b6b27 100644
--- a/vlib/crypto/sha1/sha1.v
+++ b/vlib/crypto/sha1/sha1.v
@@ -115,16 +115,16 @@ fn (d mut Digest) checksum() []byte {
 
 	// Length in bits.
 	len <<= u64(3)
-	binary.big_endian_put_u64(tmp, len)
-	d.write(tmp.left(8))
+	binary.big_endian_put_u64(mut tmp, len)
+	d.write(mut tmp.left(8))
 
 	mut digest := [byte(0); Size]
 
-	binary.big_endian_put_u32(digest, d.h[0])
-	binary.big_endian_put_u32(digest.right(4), d.h[1])
-	binary.big_endian_put_u32(digest.right(8), d.h[2])
-	binary.big_endian_put_u32(digest.right(12), d.h[3])
-	binary.big_endian_put_u32(digest.right(16), d.h[4])
+	binary.big_endian_put_u32(mut digest, d.h[0])
+	binary.big_endian_put_u32(mut digest.right(4), d.h[1])
+	binary.big_endian_put_u32(mut digest.right(8), d.h[2])
+	binary.big_endian_put_u32(mut digest.right(12), d.h[3])
+	binary.big_endian_put_u32(mut digest.right(16), d.h[4])
 
 	return digest
 }
@@ -132,7 +132,7 @@ fn (d mut Digest) checksum() []byte {
 // Sum returns the SHA-1 checksum of the data.
 pub fn sum(data []byte) []byte {
 	mut d := new()
-	d.write(data)
+	d.write(mut data)
 	return d.checksum()
 }
 
diff --git a/vlib/crypto/sha256/sha256.v b/vlib/crypto/sha256/sha256.v
index 083796b5aa..34f167c7c2 100644
--- a/vlib/crypto/sha256/sha256.v
+++ b/vlib/crypto/sha256/sha256.v
@@ -99,7 +99,7 @@ fn (d mut Digest) write(p mut []byte) ?int {
 		n := copy(d.x.right(d.nx), p)
 		d.nx += n
 		if d.nx == Chunk {
-			block(d, d.x)
+			block(mut d, d.x)
 			d.nx = 0
 		}
 		if n >= p.len {
@@ -110,7 +110,7 @@ fn (d mut Digest) write(p mut []byte) ?int {
 	}
 	if p.len >= Chunk {
 		n := p.len &~ (Chunk - 1)
-		block(d, p.left(n))
+		block(mut d, p.left(n))
 		if n >= p.len {
 			p = []byte
 		} else {
@@ -153,7 +153,7 @@ fn (d mut Digest) checksum() []byte {
 	// Length in bits.
 	len <<= u64(3)
 	binary.big_endian_put_u64(mut tmp, len)
-	d.write(tmp.left(8))
+	d.write(mut tmp.left(8))
 
 	if d.nx != 0 {
 		panic('d.nx != 0')
@@ -169,7 +169,7 @@ fn (d mut Digest) checksum() []byte {
 	binary.big_endian_put_u32(mut digest.right(20), d.h[5])
 	binary.big_endian_put_u32(mut digest.right(24), d.h[6])
 	if !d.is224 {
-		binary.big_endian_put_u32(digest.right(28), d.h[7])
+		binary.big_endian_put_u32(mut digest.right(28), d.h[7])
 	}
 
 	return digest
@@ -183,24 +183,24 @@ pub fn sum(data []byte) []byte {
 // sum256 returns the SHA256 checksum of the data.
 pub fn sum256(data []byte) []byte {
 	mut d := new()
-	d.write(data)
+	d.write(mut data)
 	return d.checksum()
 }
 
 // sum224 returns the SHA224 checksum of the data.
 pub fn sum224(data []byte) []byte {
 	mut d := new224()
-	d.write(data)
+	d.write(mut data)
 	sum := d.checksum()
 	mut sum224 := [byte(0); Size224]
 	copy(sum224, sum.left(Size224))
 	return sum224
 }
 
-fn block(dig &Digest, p []byte) {
+fn block(dig mut Digest, p []byte) {
 	// For now just use block_generic until we have specific
 	// architecture optimized versions
-	block_generic(dig, p)
+	block_generic(mut dig, p)
 }
 
 pub fn (d &Digest) size() int {
diff --git a/vlib/crypto/sha512/sha512.v b/vlib/crypto/sha512/sha512.v
index 7dd80b473a..1cf0d2a511 100644
--- a/vlib/crypto/sha512/sha512.v
+++ b/vlib/crypto/sha512/sha512.v
@@ -146,8 +146,7 @@ fn new384() *Digest {
 	return _new(crypto.Hash.SHA384)
 }
 
-fn (d mut Digest) write(p_ []byte) ?int {
-	mut p := p_ 
+fn (d mut Digest) write(p mut []byte) ?int {
 	nn := p.len
 	d.len += u64(nn)
 	if d.nx > 0 {
@@ -210,9 +209,9 @@ fn (d mut Digest) checksum() []byte {
 	tmp[0] = 0x80
 
 	if int(len)%128 < 112 {
-		d.write(tmp.left(112-int(len)%128))
+		d.write(mut tmp.left(112-int(len)%128))
 	} else {
-		d.write(tmp.left(128+112-int(len)%128))
+		d.write(mut tmp.left(128+112-int(len)%128))
 	}
 
 	// Length in bits.
@@ -220,7 +219,7 @@ fn (d mut Digest) checksum() []byte {
 
 	binary.big_endian_put_u64(mut tmp, u64(0)) // upper 64 bits are always zero, because len variable has type u64
 	binary.big_endian_put_u64(mut tmp.right(8), len)
-	d.write(tmp.left(16))
+	d.write(mut tmp.left(16))
 
 	if d.nx != 0 {
 		panic('d.nx != 0')
@@ -245,14 +244,14 @@ fn (d mut Digest) checksum() []byte {
 // sum512 returns the SHA512 checksum of the data.
 pub fn sum512(data []byte) []byte {
 	mut d := _new(crypto.Hash.SHA512)
-	d.write(data)
+	d.write(mut data)
 	return d.checksum()
 }
 
 // sum384 returns the SHA384 checksum of the data.
 pub fn sum384(data []byte) []byte {
 	mut d := _new(crypto.Hash.SHA384)
-	d.write(data)
+	d.write(mut data)
 	sum := d.checksum()
 	mut sum384 := [byte(0); Size384]
 	copy(sum384, sum.left(Size384))
@@ -262,7 +261,7 @@ pub fn sum384(data []byte) []byte {
 // sum512_224 returns the Sum512/224 checksum of the data.
 pub fn sum512_224(data []byte) []byte {
 	mut d := _new(crypto.Hash.SHA512_224)
-	d.write(data)
+	d.write(mut data)
 	sum := d.checksum()
 	mut sum224 := [byte(0); Size224]
 	copy(sum224, sum.left(Size224))
@@ -272,7 +271,7 @@ pub fn sum512_224(data []byte) []byte {
 // Sum512_256 returns the Sum512/256 checksum of the data.
 pub fn sum512_256(data []byte) []byte {
 	mut d := _new(crypto.Hash.SHA512_256)
-	d.write(data)
+	d.write(mut data)
 	sum := d.checksum()
 	mut sum256 := [byte(0); Size256]
 	copy(sum256, sum.left(Size256))
@@ -282,7 +281,7 @@ pub fn sum512_256(data []byte) []byte {
 fn block(dig mut Digest, p []byte) {
 	// For now just use block_generic until we have specific
 	// architecture optimized versions
-	block_generic(mut dig, p)
+	block_generic(mut dig, mut p)
 }
 
 pub fn (d &Digest) size() int {
diff --git a/vlib/crypto/sha512/sha512block_generic.v b/vlib/crypto/sha512/sha512block_generic.v
index dd9ede3e0c..e5cf405815 100644
--- a/vlib/crypto/sha512/sha512block_generic.v
+++ b/vlib/crypto/sha512/sha512block_generic.v
@@ -94,7 +94,7 @@ const(
 	]
 )
 
-fn block_generic(dig mut Digest, p []byte) {
+fn block_generic(dig mut Digest, p mut []byte) {
 	mut w := [u64(0); 80]
 	
 	mut h0 := dig.h[0]
diff --git a/vlib/glm/glm.v b/vlib/glm/glm.v
index 1932dbbc68..f64af1d8b7 100644
--- a/vlib/glm/glm.v
+++ b/vlib/glm/glm.v
@@ -250,7 +250,7 @@ pub fn identity() Mat4 {
 }
 
 // returns *f32 without allocation
-pub fn identity2(res *f32) {
+pub fn identity2(res mut *f32) {
 	res[0] = 1
 	res[5] = 1
 	res[10] = 1
diff --git a/vlib/net/urllib/urllib.v b/vlib/net/urllib/urllib.v
index 573d57f8aa..620a5c35cb 100644
--- a/vlib/net/urllib/urllib.v
+++ b/vlib/net/urllib/urllib.v
@@ -824,14 +824,15 @@ fn parse_query_silent(query string) Values {
 
 fn _parse_query(m mut Values, query string) ?bool {
 	mut had_error := false
-	for query != '' {
-		mut key := query
+	mut q := query
+	for q != '' {
+		mut key := q
 		mut i := key.index_any('&;')
 		if i >= 0 {
-			query = key.right(i+1)
+			q = key.right(i+1)
 			key = key.left(i)
 		} else {
-			query = ''
+			q = ''
 		}
 		if key == '' {
 			continue